diff --git a/Jellyfin.Api/Controllers/AlbumsController.cs b/Jellyfin.Api/Controllers/AlbumsController.cs
index 622123873d..70315b0a33 100644
--- a/Jellyfin.Api/Controllers/AlbumsController.cs
+++ b/Jellyfin.Api/Controllers/AlbumsController.cs
@@ -53,7 +53,7 @@ namespace Jellyfin.Api.Controllers
         public ActionResult<QueryResult<BaseItemDto>> GetSimilarAlbums(
             [FromRoute] string albumId,
             [FromQuery] Guid userId,
-            [FromQuery] string excludeArtistIds,
+            [FromQuery] string? excludeArtistIds,
             [FromQuery] int? limit)
         {
             var dtoOptions = new DtoOptions().AddClientFields(Request);
@@ -85,7 +85,7 @@ namespace Jellyfin.Api.Controllers
         public ActionResult<QueryResult<BaseItemDto>> GetSimilarArtists(
             [FromRoute] string artistId,
             [FromQuery] Guid userId,
-            [FromQuery] string excludeArtistIds,
+            [FromQuery] string? excludeArtistIds,
             [FromQuery] int? limit)
         {
             var dtoOptions = new DtoOptions().AddClientFields(Request);
diff --git a/Jellyfin.Api/Controllers/ApiKeyController.cs b/Jellyfin.Api/Controllers/ApiKeyController.cs
index ed521c1fc5..fef4d7262d 100644
--- a/Jellyfin.Api/Controllers/ApiKeyController.cs
+++ b/Jellyfin.Api/Controllers/ApiKeyController.cs
@@ -65,7 +65,7 @@ namespace Jellyfin.Api.Controllers
         [HttpPost("Keys")]
         [Authorize(Policy = Policies.RequiresElevation)]
         [ProducesResponseType(StatusCodes.Status204NoContent)]
-        public ActionResult CreateKey([FromQuery, Required] string app)
+        public ActionResult CreateKey([FromQuery, Required] string? app)
         {
             _authRepo.Create(new AuthenticationInfo
             {
@@ -88,7 +88,7 @@ namespace Jellyfin.Api.Controllers
         [HttpDelete("Keys/{key}")]
         [Authorize(Policy = Policies.RequiresElevation)]
         [ProducesResponseType(StatusCodes.Status204NoContent)]
-        public ActionResult RevokeKey([FromRoute] string key)
+        public ActionResult RevokeKey([FromRoute] string? key)
         {
             _sessionManager.RevokeToken(key);
             return NoContent();
diff --git a/Jellyfin.Api/Controllers/CollectionController.cs b/Jellyfin.Api/Controllers/CollectionController.cs
index 29db0b1782..7ff98b2513 100644
--- a/Jellyfin.Api/Controllers/CollectionController.cs
+++ b/Jellyfin.Api/Controllers/CollectionController.cs
@@ -51,8 +51,8 @@ namespace Jellyfin.Api.Controllers
         [HttpPost]
         [ProducesResponseType(StatusCodes.Status200OK)]
         public ActionResult<CollectionCreationResult> CreateCollection(
-            [FromQuery] string name,
-            [FromQuery] string ids,
+            [FromQuery] string? name,
+            [FromQuery] string? ids,
             [FromQuery] bool isLocked,
             [FromQuery] Guid? parentId)
         {
@@ -86,7 +86,7 @@ namespace Jellyfin.Api.Controllers
         /// <returns>A <see cref="NoContentResult"/> indicating success.</returns>
         [HttpPost("{collectionId}/Items")]
         [ProducesResponseType(StatusCodes.Status204NoContent)]
-        public ActionResult AddToCollection([FromRoute] Guid collectionId, [FromQuery] string itemIds)
+        public ActionResult AddToCollection([FromRoute] Guid collectionId, [FromQuery] string? itemIds)
         {
             _collectionManager.AddToCollection(collectionId, RequestHelpers.Split(itemIds, ',', true));
             return NoContent();
@@ -101,7 +101,7 @@ namespace Jellyfin.Api.Controllers
         /// <returns>A <see cref="NoContentResult"/> indicating success.</returns>
         [HttpDelete("{collectionId}/Items")]
         [ProducesResponseType(StatusCodes.Status204NoContent)]
-        public ActionResult RemoveFromCollection([FromRoute] Guid collectionId, [FromQuery] string itemIds)
+        public ActionResult RemoveFromCollection([FromRoute] Guid collectionId, [FromQuery] string? itemIds)
         {
             _collectionManager.RemoveFromCollection(collectionId, RequestHelpers.Split(itemIds, ',', true));
             return NoContent();
diff --git a/Jellyfin.Api/Controllers/ConfigurationController.cs b/Jellyfin.Api/Controllers/ConfigurationController.cs
index d275ed2eba..13933cb33b 100644
--- a/Jellyfin.Api/Controllers/ConfigurationController.cs
+++ b/Jellyfin.Api/Controllers/ConfigurationController.cs
@@ -70,7 +70,7 @@ namespace Jellyfin.Api.Controllers
         /// <returns>Configuration.</returns>
         [HttpGet("Configuration/{key}")]
         [ProducesResponseType(StatusCodes.Status200OK)]
-        public ActionResult<object> GetNamedConfiguration([FromRoute] string key)
+        public ActionResult<object> GetNamedConfiguration([FromRoute] string? key)
         {
             return _configurationManager.GetConfiguration(key);
         }
@@ -84,7 +84,7 @@ namespace Jellyfin.Api.Controllers
         [HttpPost("Configuration/{key}")]
         [Authorize(Policy = Policies.RequiresElevation)]
         [ProducesResponseType(StatusCodes.Status204NoContent)]
-        public async Task<ActionResult> UpdateNamedConfiguration([FromRoute] string key)
+        public async Task<ActionResult> UpdateNamedConfiguration([FromRoute] string? key)
         {
             var configurationType = _configurationManager.GetConfigurationType(key);
             var configuration = await JsonSerializer.DeserializeAsync(Request.Body, configurationType).ConfigureAwait(false);
diff --git a/Jellyfin.Api/Controllers/DashboardController.cs b/Jellyfin.Api/Controllers/DashboardController.cs
index 6cfee2463f..699ef6bf7b 100644
--- a/Jellyfin.Api/Controllers/DashboardController.cs
+++ b/Jellyfin.Api/Controllers/DashboardController.cs
@@ -122,7 +122,7 @@ namespace Jellyfin.Api.Controllers
         [HttpGet("/web/ConfigurationPage")]
         [ProducesResponseType(StatusCodes.Status200OK)]
         [ProducesResponseType(StatusCodes.Status404NotFound)]
-        public ActionResult GetDashboardConfigurationPage([FromQuery] string name)
+        public ActionResult GetDashboardConfigurationPage([FromQuery] string? name)
         {
             IPlugin? plugin = null;
             Stream? stream = null;
diff --git a/Jellyfin.Api/Controllers/DevicesController.cs b/Jellyfin.Api/Controllers/DevicesController.cs
index 55ca7b7c0f..3cf7b33785 100644
--- a/Jellyfin.Api/Controllers/DevicesController.cs
+++ b/Jellyfin.Api/Controllers/DevicesController.cs
@@ -65,7 +65,7 @@ namespace Jellyfin.Api.Controllers
         [Authorize(Policy = Policies.RequiresElevation)]
         [ProducesResponseType(StatusCodes.Status200OK)]
         [ProducesResponseType(StatusCodes.Status404NotFound)]
-        public ActionResult<DeviceInfo> GetDeviceInfo([FromQuery, BindRequired] string id)
+        public ActionResult<DeviceInfo> GetDeviceInfo([FromQuery, BindRequired] string? id)
         {
             var deviceInfo = _deviceManager.GetDevice(id);
             if (deviceInfo == null)
@@ -87,7 +87,7 @@ namespace Jellyfin.Api.Controllers
         [Authorize(Policy = Policies.RequiresElevation)]
         [ProducesResponseType(StatusCodes.Status200OK)]
         [ProducesResponseType(StatusCodes.Status404NotFound)]
-        public ActionResult<DeviceOptions> GetDeviceOptions([FromQuery, BindRequired] string id)
+        public ActionResult<DeviceOptions> GetDeviceOptions([FromQuery, BindRequired] string? id)
         {
             var deviceInfo = _deviceManager.GetDeviceOptions(id);
             if (deviceInfo == null)
@@ -111,7 +111,7 @@ namespace Jellyfin.Api.Controllers
         [ProducesResponseType(StatusCodes.Status204NoContent)]
         [ProducesResponseType(StatusCodes.Status404NotFound)]
         public ActionResult UpdateDeviceOptions(
-            [FromQuery, BindRequired] string id,
+            [FromQuery, BindRequired] string? id,
             [FromBody, BindRequired] DeviceOptions deviceOptions)
         {
             var existingDeviceOptions = _deviceManager.GetDeviceOptions(id);
@@ -134,7 +134,7 @@ namespace Jellyfin.Api.Controllers
         [HttpDelete]
         [ProducesResponseType(StatusCodes.Status204NoContent)]
         [ProducesResponseType(StatusCodes.Status404NotFound)]
-        public ActionResult DeleteDevice([FromQuery, BindRequired] string id)
+        public ActionResult DeleteDevice([FromQuery, BindRequired] string? id)
         {
             var existingDevice = _deviceManager.GetDevice(id);
             if (existingDevice == null)
diff --git a/Jellyfin.Api/Controllers/DisplayPreferencesController.cs b/Jellyfin.Api/Controllers/DisplayPreferencesController.cs
index 3f946d9d22..1255e6dab0 100644
--- a/Jellyfin.Api/Controllers/DisplayPreferencesController.cs
+++ b/Jellyfin.Api/Controllers/DisplayPreferencesController.cs
@@ -39,9 +39,9 @@ namespace Jellyfin.Api.Controllers
         [HttpGet("{displayPreferencesId}")]
         [ProducesResponseType(StatusCodes.Status200OK)]
         public ActionResult<DisplayPreferences> GetDisplayPreferences(
-            [FromRoute] string displayPreferencesId,
-            [FromQuery] [Required] string userId,
-            [FromQuery] [Required] string client)
+            [FromRoute] string? displayPreferencesId,
+            [FromQuery] [Required] string? userId,
+            [FromQuery] [Required] string? client)
         {
             return _displayPreferencesRepository.GetDisplayPreferences(displayPreferencesId, userId, client);
         }
@@ -59,9 +59,9 @@ namespace Jellyfin.Api.Controllers
         [ProducesResponseType(StatusCodes.Status204NoContent)]
         [SuppressMessage("Microsoft.Performance", "CA1801:ReviewUnusedParameters", MessageId = "displayPreferencesId", Justification = "Imported from ServiceStack")]
         public ActionResult UpdateDisplayPreferences(
-            [FromRoute] string displayPreferencesId,
-            [FromQuery, BindRequired] string userId,
-            [FromQuery, BindRequired] string client,
+            [FromRoute] string? displayPreferencesId,
+            [FromQuery, BindRequired] string? userId,
+            [FromQuery, BindRequired] string? client,
             [FromBody, BindRequired] DisplayPreferences displayPreferences)
         {
             _displayPreferencesRepository.SaveDisplayPreferences(
diff --git a/Jellyfin.Api/Controllers/ImageByNameController.cs b/Jellyfin.Api/Controllers/ImageByNameController.cs
index 4800c0608f..5244c35b89 100644
--- a/Jellyfin.Api/Controllers/ImageByNameController.cs
+++ b/Jellyfin.Api/Controllers/ImageByNameController.cs
@@ -64,7 +64,7 @@ namespace Jellyfin.Api.Controllers
         [Produces(MediaTypeNames.Application.Octet)]
         [ProducesResponseType(StatusCodes.Status200OK)]
         [ProducesResponseType(StatusCodes.Status404NotFound)]
-        public ActionResult<FileStreamResult> GetGeneralImage([FromRoute] string name, [FromRoute] string type)
+        public ActionResult<FileStreamResult> GetGeneralImage([FromRoute] string? name, [FromRoute] string? type)
         {
             var filename = string.Equals(type, "primary", StringComparison.OrdinalIgnoreCase)
                 ? "folder"
@@ -110,8 +110,8 @@ namespace Jellyfin.Api.Controllers
         [ProducesResponseType(StatusCodes.Status200OK)]
         [ProducesResponseType(StatusCodes.Status404NotFound)]
         public ActionResult<FileStreamResult> GetRatingImage(
-            [FromRoute] string theme,
-            [FromRoute] string name)
+            [FromRoute] string? theme,
+            [FromRoute] string? name)
         {
             return GetImageFile(_applicationPaths.RatingsPath, theme, name);
         }
@@ -143,8 +143,8 @@ namespace Jellyfin.Api.Controllers
         [ProducesResponseType(StatusCodes.Status200OK)]
         [ProducesResponseType(StatusCodes.Status404NotFound)]
         public ActionResult<FileStreamResult> GetMediaInfoImage(
-            [FromRoute] string theme,
-            [FromRoute] string name)
+            [FromRoute] string? theme,
+            [FromRoute] string? name)
         {
             return GetImageFile(_applicationPaths.MediaInfoImagesPath, theme, name);
         }
@@ -156,7 +156,7 @@ namespace Jellyfin.Api.Controllers
         /// <param name="theme">Theme to search.</param>
         /// <param name="name">File name to search for.</param>
         /// <returns>A <see cref="FileStreamResult"/> containing the image contents on success, or a <see cref="NotFoundResult"/> if the image could not be found.</returns>
-        private ActionResult<FileStreamResult> GetImageFile(string basePath, string theme, string name)
+        private ActionResult<FileStreamResult> GetImageFile(string basePath, string? theme, string? name)
         {
             var themeFolder = Path.Combine(basePath, theme);
             if (Directory.Exists(themeFolder))
diff --git a/Jellyfin.Api/Controllers/InstantMixController.cs b/Jellyfin.Api/Controllers/InstantMixController.cs
index f1ff770a40..9d945fe2b0 100644
--- a/Jellyfin.Api/Controllers/InstantMixController.cs
+++ b/Jellyfin.Api/Controllers/InstantMixController.cs
@@ -65,7 +65,7 @@ namespace Jellyfin.Api.Controllers
             [FromRoute] Guid id,
             [FromQuery] Guid userId,
             [FromQuery] int? limit,
-            [FromQuery] string fields,
+            [FromQuery] string? fields,
             [FromQuery] bool? enableImages,
             [FromQuery] bool? enableUserData,
             [FromQuery] int? imageTypeLimit,
@@ -100,7 +100,7 @@ namespace Jellyfin.Api.Controllers
             [FromRoute] Guid id,
             [FromQuery] Guid userId,
             [FromQuery] int? limit,
-            [FromQuery] string fields,
+            [FromQuery] string? fields,
             [FromQuery] bool? enableImages,
             [FromQuery] bool? enableUserData,
             [FromQuery] int? imageTypeLimit,
@@ -135,7 +135,7 @@ namespace Jellyfin.Api.Controllers
             [FromRoute] Guid id,
             [FromQuery] Guid userId,
             [FromQuery] int? limit,
-            [FromQuery] string fields,
+            [FromQuery] string? fields,
             [FromQuery] bool? enableImages,
             [FromQuery] bool? enableUserData,
             [FromQuery] int? imageTypeLimit,
@@ -167,10 +167,10 @@ namespace Jellyfin.Api.Controllers
         [HttpGet("/MusicGenres/{name}/InstantMix")]
         [ProducesResponseType(StatusCodes.Status200OK)]
         public ActionResult<QueryResult<BaseItemDto>> GetInstantMixFromMusicGenre(
-            [FromRoute] string name,
+            [FromRoute] string? name,
             [FromQuery] Guid userId,
             [FromQuery] int? limit,
-            [FromQuery] string fields,
+            [FromQuery] string? fields,
             [FromQuery] bool? enableImages,
             [FromQuery] bool? enableUserData,
             [FromQuery] int? imageTypeLimit,
@@ -204,7 +204,7 @@ namespace Jellyfin.Api.Controllers
             [FromRoute] Guid id,
             [FromQuery] Guid userId,
             [FromQuery] int? limit,
-            [FromQuery] string fields,
+            [FromQuery] string? fields,
             [FromQuery] bool? enableImages,
             [FromQuery] bool? enableUserData,
             [FromQuery] int? imageTypeLimit,
@@ -239,7 +239,7 @@ namespace Jellyfin.Api.Controllers
             [FromRoute] Guid id,
             [FromQuery] Guid userId,
             [FromQuery] int? limit,
-            [FromQuery] string fields,
+            [FromQuery] string? fields,
             [FromQuery] bool? enableImages,
             [FromQuery] bool? enableUserData,
             [FromQuery] int? imageTypeLimit,
@@ -274,7 +274,7 @@ namespace Jellyfin.Api.Controllers
             [FromRoute] Guid id,
             [FromQuery] Guid userId,
             [FromQuery] int? limit,
-            [FromQuery] string fields,
+            [FromQuery] string? fields,
             [FromQuery] bool? enableImages,
             [FromQuery] bool? enableUserData,
             [FromQuery] int? imageTypeLimit,
diff --git a/Jellyfin.Api/Controllers/ItemUpdateController.cs b/Jellyfin.Api/Controllers/ItemUpdateController.cs
index 384f250ecc..c9b2aafcca 100644
--- a/Jellyfin.Api/Controllers/ItemUpdateController.cs
+++ b/Jellyfin.Api/Controllers/ItemUpdateController.cs
@@ -193,7 +193,7 @@ namespace Jellyfin.Api.Controllers
         [HttpPost("/Items/{itemId}/ContentType")]
         [ProducesResponseType(StatusCodes.Status204NoContent)]
         [ProducesResponseType(StatusCodes.Status404NotFound)]
-        public ActionResult UpdateItemContentType([FromRoute] Guid itemId, [FromQuery, BindRequired] string contentType)
+        public ActionResult UpdateItemContentType([FromRoute] Guid itemId, [FromQuery, BindRequired] string? contentType)
         {
             var item = _libraryManager.GetItemById(itemId);
             if (item == null)
diff --git a/Jellyfin.Api/Controllers/LibraryController.cs b/Jellyfin.Api/Controllers/LibraryController.cs
index 1ecf2ac737..f1106cda60 100644
--- a/Jellyfin.Api/Controllers/LibraryController.cs
+++ b/Jellyfin.Api/Controllers/LibraryController.cs
@@ -524,7 +524,7 @@ namespace Jellyfin.Api.Controllers
         [HttpPost("/Library/Series/Updated")]
         [Authorize(Policy = Policies.DefaultAuthorization)]
         [ProducesResponseType(StatusCodes.Status204NoContent)]
-        public ActionResult PostUpdatedSeries([FromQuery] string tvdbId)
+        public ActionResult PostUpdatedSeries([FromQuery] string? tvdbId)
         {
             var series = _libraryManager.GetItemList(new InternalItemsQuery
             {
@@ -554,7 +554,7 @@ namespace Jellyfin.Api.Controllers
         [HttpPost("/Library/Movies/Updated")]
         [Authorize(Policy = Policies.DefaultAuthorization)]
         [ProducesResponseType(StatusCodes.Status204NoContent)]
-        public ActionResult PostUpdatedMovies([FromRoute] string tmdbId, [FromRoute] string imdbId)
+        public ActionResult PostUpdatedMovies([FromRoute] string? tmdbId, [FromRoute] string? imdbId)
         {
             var movies = _libraryManager.GetItemList(new InternalItemsQuery
             {
@@ -687,10 +687,10 @@ namespace Jellyfin.Api.Controllers
         [ProducesResponseType(StatusCodes.Status200OK)]
         public ActionResult<QueryResult<BaseItemDto>> GetSimilarItems(
             [FromRoute] Guid itemId,
-            [FromQuery] string excludeArtistIds,
+            [FromQuery] string? excludeArtistIds,
             [FromQuery] Guid userId,
             [FromQuery] int? limit,
-            [FromQuery] string fields)
+            [FromQuery] string? fields)
         {
             var item = itemId.Equals(Guid.Empty)
                 ? (!userId.Equals(Guid.Empty)
@@ -737,7 +737,7 @@ namespace Jellyfin.Api.Controllers
         [HttpGet("/Libraries/AvailableOptions")]
         [Authorize(Policy = Policies.FirstTimeSetupOrElevated)]
         [ProducesResponseType(StatusCodes.Status200OK)]
-        public ActionResult<LibraryOptionsResultDto> GetLibraryOptionsInfo([FromQuery] string libraryContentType, [FromQuery] bool isNewLibrary)
+        public ActionResult<LibraryOptionsResultDto> GetLibraryOptionsInfo([FromQuery] string? libraryContentType, [FromQuery] bool isNewLibrary)
         {
             var result = new LibraryOptionsResultDto();
 
@@ -877,10 +877,10 @@ namespace Jellyfin.Api.Controllers
 
         private QueryResult<BaseItemDto> GetSimilarItemsResult(
             BaseItem item,
-            string excludeArtistIds,
+            string? excludeArtistIds,
             Guid userId,
             int? limit,
-            string fields,
+            string? fields,
             string[] includeItemTypes,
             bool isMovie)
         {
@@ -942,7 +942,7 @@ namespace Jellyfin.Api.Controllers
             return result;
         }
 
-        private static string[] GetRepresentativeItemTypes(string contentType)
+        private static string[] GetRepresentativeItemTypes(string? contentType)
         {
             return contentType switch
             {
diff --git a/Jellyfin.Api/Controllers/LibraryStructureController.cs b/Jellyfin.Api/Controllers/LibraryStructureController.cs
index e4ac019c9a..0c91f84477 100644
--- a/Jellyfin.Api/Controllers/LibraryStructureController.cs
+++ b/Jellyfin.Api/Controllers/LibraryStructureController.cs
@@ -72,8 +72,8 @@ namespace Jellyfin.Api.Controllers
         [HttpPost]
         [ProducesResponseType(StatusCodes.Status204NoContent)]
         public async Task<ActionResult> AddVirtualFolder(
-            [FromQuery] string name,
-            [FromQuery] string collectionType,
+            [FromQuery] string? name,
+            [FromQuery] string? collectionType,
             [FromQuery] bool refreshLibrary,
             [FromQuery] string[] paths,
             [FromQuery] LibraryOptions libraryOptions)
@@ -100,7 +100,7 @@ namespace Jellyfin.Api.Controllers
         [HttpDelete]
         [ProducesResponseType(StatusCodes.Status204NoContent)]
         public async Task<ActionResult> RemoveVirtualFolder(
-            [FromQuery] string name,
+            [FromQuery] string? name,
             [FromQuery] bool refreshLibrary)
         {
             await _libraryManager.RemoveVirtualFolder(name, refreshLibrary).ConfigureAwait(false);
@@ -123,8 +123,8 @@ namespace Jellyfin.Api.Controllers
         [ProducesResponseType(StatusCodes.Status404NotFound)]
         [ProducesResponseType(StatusCodes.Status409Conflict)]
         public ActionResult RenameVirtualFolder(
-            [FromQuery] string name,
-            [FromQuery] string newName,
+            [FromQuery] string? name,
+            [FromQuery] string? newName,
             [FromQuery] bool refreshLibrary)
         {
             if (string.IsNullOrWhiteSpace(name))
@@ -205,8 +205,8 @@ namespace Jellyfin.Api.Controllers
         [HttpPost("Paths")]
         [ProducesResponseType(StatusCodes.Status204NoContent)]
         public ActionResult AddMediaPath(
-            [FromQuery] string name,
-            [FromQuery] string path,
+            [FromQuery] string? name,
+            [FromQuery] string? path,
             [FromQuery] MediaPathInfo pathInfo,
             [FromQuery] bool refreshLibrary)
         {
@@ -256,7 +256,7 @@ namespace Jellyfin.Api.Controllers
         [HttpPost("Paths/Update")]
         [ProducesResponseType(StatusCodes.Status204NoContent)]
         public ActionResult UpdateMediaPath(
-            [FromQuery] string name,
+            [FromQuery] string? name,
             [FromQuery] MediaPathInfo pathInfo)
         {
             if (string.IsNullOrWhiteSpace(name))
@@ -280,8 +280,8 @@ namespace Jellyfin.Api.Controllers
         [HttpDelete("Paths")]
         [ProducesResponseType(StatusCodes.Status204NoContent)]
         public ActionResult RemoveMediaPath(
-            [FromQuery] string name,
-            [FromQuery] string path,
+            [FromQuery] string? name,
+            [FromQuery] string? path,
             [FromQuery] bool refreshLibrary)
         {
             if (string.IsNullOrWhiteSpace(name))
@@ -327,7 +327,7 @@ namespace Jellyfin.Api.Controllers
         [HttpPost("LibraryOptions")]
         [ProducesResponseType(StatusCodes.Status204NoContent)]
         public ActionResult UpdateLibraryOptions(
-            [FromQuery] string id,
+            [FromQuery] string? id,
             [FromQuery] LibraryOptions libraryOptions)
         {
             var collectionFolder = (CollectionFolder)_libraryManager.GetItemById(id);
diff --git a/Jellyfin.Api/Controllers/NotificationsController.cs b/Jellyfin.Api/Controllers/NotificationsController.cs
index cfa7545c96..02aa39b248 100644
--- a/Jellyfin.Api/Controllers/NotificationsController.cs
+++ b/Jellyfin.Api/Controllers/NotificationsController.cs
@@ -93,8 +93,8 @@ namespace Jellyfin.Api.Controllers
         [HttpPost("Admin")]
         [ProducesResponseType(StatusCodes.Status204NoContent)]
         public ActionResult CreateAdminNotification(
-            [FromQuery] string name,
-            [FromQuery] string description,
+            [FromQuery] string? name,
+            [FromQuery] string? description,
             [FromQuery] string? url,
             [FromQuery] NotificationLevel? level)
         {
diff --git a/Jellyfin.Api/Controllers/PackageController.cs b/Jellyfin.Api/Controllers/PackageController.cs
index 486575d23a..68ae05658e 100644
--- a/Jellyfin.Api/Controllers/PackageController.cs
+++ b/Jellyfin.Api/Controllers/PackageController.cs
@@ -40,7 +40,7 @@ namespace Jellyfin.Api.Controllers
         [HttpGet("/{name}")]
         [ProducesResponseType(StatusCodes.Status200OK)]
         public async Task<ActionResult<PackageInfo>> GetPackageInfo(
-            [FromRoute] [Required] string name,
+            [FromRoute] [Required] string? name,
             [FromQuery] string? assemblyGuid)
         {
             var packages = await _installationManager.GetAvailablePackages().ConfigureAwait(false);
@@ -80,9 +80,9 @@ namespace Jellyfin.Api.Controllers
         [ProducesResponseType(StatusCodes.Status404NotFound)]
         [Authorize(Policy = Policies.RequiresElevation)]
         public async Task<ActionResult> InstallPackage(
-            [FromRoute] [Required] string name,
-            [FromQuery] string assemblyGuid,
-            [FromQuery] string version)
+            [FromRoute] [Required] string? name,
+            [FromQuery] string? assemblyGuid,
+            [FromQuery] string? version)
         {
             var packages = await _installationManager.GetAvailablePackages().ConfigureAwait(false);
             var package = _installationManager.GetCompatibleVersions(
diff --git a/Jellyfin.Api/Controllers/PlaylistsController.cs b/Jellyfin.Api/Controllers/PlaylistsController.cs
index 2dc0d2dc71..d62404fc93 100644
--- a/Jellyfin.Api/Controllers/PlaylistsController.cs
+++ b/Jellyfin.Api/Controllers/PlaylistsController.cs
@@ -84,8 +84,8 @@ namespace Jellyfin.Api.Controllers
         [HttpPost("{playlistId}/Items")]
         [ProducesResponseType(StatusCodes.Status204NoContent)]
         public ActionResult AddToPlaylist(
-            [FromRoute] string playlistId,
-            [FromQuery] string ids,
+            [FromRoute] string? playlistId,
+            [FromQuery] string? ids,
             [FromQuery] Guid userId)
         {
             _playlistManager.AddToPlaylist(playlistId, RequestHelpers.GetGuids(ids), userId);
@@ -103,8 +103,8 @@ namespace Jellyfin.Api.Controllers
         [HttpPost("{playlistId}/Items/{itemId}/Move/{newIndex}")]
         [ProducesResponseType(StatusCodes.Status204NoContent)]
         public ActionResult MoveItem(
-            [FromRoute] string playlistId,
-            [FromRoute] string itemId,
+            [FromRoute] string? playlistId,
+            [FromRoute] string? itemId,
             [FromRoute] int newIndex)
         {
             _playlistManager.MoveItem(playlistId, itemId, newIndex);
@@ -120,7 +120,7 @@ namespace Jellyfin.Api.Controllers
         /// <returns>An <see cref="NoContentResult"/> on success.</returns>
         [HttpDelete("{playlistId}/Items")]
         [ProducesResponseType(StatusCodes.Status204NoContent)]
-        public ActionResult RemoveFromPlaylist([FromRoute] string playlistId, [FromQuery] string entryIds)
+        public ActionResult RemoveFromPlaylist([FromRoute] string? playlistId, [FromQuery] string? entryIds)
         {
             _playlistManager.RemoveFromPlaylist(playlistId, RequestHelpers.Split(entryIds, ',', true));
             return NoContent();
@@ -147,11 +147,11 @@ namespace Jellyfin.Api.Controllers
             [FromRoute] Guid userId,
             [FromRoute] int? startIndex,
             [FromRoute] int? limit,
-            [FromRoute] string fields,
+            [FromRoute] string? fields,
             [FromRoute] bool? enableImages,
             [FromRoute] bool? enableUserData,
             [FromRoute] int? imageTypeLimit,
-            [FromRoute] string enableImageTypes)
+            [FromRoute] string? enableImageTypes)
         {
             var playlist = (Playlist)_libraryManager.GetItemById(playlistId);
             if (playlist == null)
diff --git a/Jellyfin.Api/Controllers/PluginsController.cs b/Jellyfin.Api/Controllers/PluginsController.cs
index fd48983ea7..056395a51d 100644
--- a/Jellyfin.Api/Controllers/PluginsController.cs
+++ b/Jellyfin.Api/Controllers/PluginsController.cs
@@ -166,7 +166,7 @@ namespace Jellyfin.Api.Controllers
         [Obsolete("This endpoint should not be used.")]
         [HttpPost("RegistrationRecords/{name}")]
         [ProducesResponseType(StatusCodes.Status200OK)]
-        public ActionResult<MBRegistrationRecord> GetRegistrationStatus([FromRoute] string name)
+        public ActionResult<MBRegistrationRecord> GetRegistrationStatus([FromRoute] string? name)
         {
             return new MBRegistrationRecord
             {
@@ -188,7 +188,7 @@ namespace Jellyfin.Api.Controllers
         [Obsolete("Paid plugins are not supported")]
         [HttpGet("/Registrations/{name}")]
         [ProducesResponseType(StatusCodes.Status501NotImplemented)]
-        public ActionResult GetRegistration([FromRoute] string name)
+        public ActionResult GetRegistration([FromRoute] string? name)
         {
             // TODO Once we have proper apps and plugins and decide to break compatibility with paid plugins,
             // delete all these registration endpoints. They are only kept for compatibility.
diff --git a/Jellyfin.Api/Controllers/RemoteImageController.cs b/Jellyfin.Api/Controllers/RemoteImageController.cs
index a0d14be7a5..6fff301297 100644
--- a/Jellyfin.Api/Controllers/RemoteImageController.cs
+++ b/Jellyfin.Api/Controllers/RemoteImageController.cs
@@ -208,7 +208,7 @@ namespace Jellyfin.Api.Controllers
         public async Task<ActionResult> DownloadRemoteImage(
             [FromRoute] Guid itemId,
             [FromQuery, BindRequired] ImageType type,
-            [FromQuery] string imageUrl)
+            [FromQuery] string? imageUrl)
         {
             var item = _libraryManager.GetItemById(itemId);
             if (item == null)
diff --git a/Jellyfin.Api/Controllers/ScheduledTasksController.cs b/Jellyfin.Api/Controllers/ScheduledTasksController.cs
index bf5c3076e0..3df325e3ba 100644
--- a/Jellyfin.Api/Controllers/ScheduledTasksController.cs
+++ b/Jellyfin.Api/Controllers/ScheduledTasksController.cs
@@ -71,7 +71,7 @@ namespace Jellyfin.Api.Controllers
         [HttpGet("{taskId}")]
         [ProducesResponseType(StatusCodes.Status200OK)]
         [ProducesResponseType(StatusCodes.Status404NotFound)]
-        public ActionResult<TaskInfo> GetTask([FromRoute] string taskId)
+        public ActionResult<TaskInfo> GetTask([FromRoute] string? taskId)
         {
             var task = _taskManager.ScheduledTasks.FirstOrDefault(i =>
                 string.Equals(i.Id, taskId, StringComparison.OrdinalIgnoreCase));
@@ -94,7 +94,7 @@ namespace Jellyfin.Api.Controllers
         [HttpPost("Running/{taskId}")]
         [ProducesResponseType(StatusCodes.Status204NoContent)]
         [ProducesResponseType(StatusCodes.Status404NotFound)]
-        public ActionResult StartTask([FromRoute] string taskId)
+        public ActionResult StartTask([FromRoute] string? taskId)
         {
             var task = _taskManager.ScheduledTasks.FirstOrDefault(o =>
                 o.Id.Equals(taskId, StringComparison.OrdinalIgnoreCase));
@@ -118,7 +118,7 @@ namespace Jellyfin.Api.Controllers
         [HttpDelete("Running/{taskId}")]
         [ProducesResponseType(StatusCodes.Status204NoContent)]
         [ProducesResponseType(StatusCodes.Status404NotFound)]
-        public ActionResult StopTask([FromRoute] string taskId)
+        public ActionResult StopTask([FromRoute] string? taskId)
         {
             var task = _taskManager.ScheduledTasks.FirstOrDefault(o =>
                 o.Id.Equals(taskId, StringComparison.OrdinalIgnoreCase));
@@ -144,7 +144,7 @@ namespace Jellyfin.Api.Controllers
         [ProducesResponseType(StatusCodes.Status204NoContent)]
         [ProducesResponseType(StatusCodes.Status404NotFound)]
         public ActionResult UpdateTask(
-            [FromRoute] string taskId,
+            [FromRoute] string? taskId,
             [FromBody, BindRequired] TaskTriggerInfo[] triggerInfos)
         {
             var task = _taskManager.ScheduledTasks.FirstOrDefault(o =>
diff --git a/Jellyfin.Api/Controllers/SearchController.cs b/Jellyfin.Api/Controllers/SearchController.cs
index d971889db8..14dc0815c7 100644
--- a/Jellyfin.Api/Controllers/SearchController.cs
+++ b/Jellyfin.Api/Controllers/SearchController.cs
@@ -81,11 +81,11 @@ namespace Jellyfin.Api.Controllers
             [FromQuery] int? startIndex,
             [FromQuery] int? limit,
             [FromQuery] Guid userId,
-            [FromQuery, Required] string searchTerm,
-            [FromQuery] string includeItemTypes,
-            [FromQuery] string excludeItemTypes,
-            [FromQuery] string mediaTypes,
-            [FromQuery] string parentId,
+            [FromQuery, Required] string? searchTerm,
+            [FromQuery] string? includeItemTypes,
+            [FromQuery] string? excludeItemTypes,
+            [FromQuery] string? mediaTypes,
+            [FromQuery] string? parentId,
             [FromQuery] bool? isMovie,
             [FromQuery] bool? isSeries,
             [FromQuery] bool? isNews,
diff --git a/Jellyfin.Api/Controllers/SessionController.cs b/Jellyfin.Api/Controllers/SessionController.cs
index 39da4178d6..bd738aa387 100644
--- a/Jellyfin.Api/Controllers/SessionController.cs
+++ b/Jellyfin.Api/Controllers/SessionController.cs
@@ -62,7 +62,7 @@ namespace Jellyfin.Api.Controllers
         [ProducesResponseType(StatusCodes.Status200OK)]
         public ActionResult<IEnumerable<SessionInfo>> GetSessions(
             [FromQuery] Guid controllableByUserId,
-            [FromQuery] string deviceId,
+            [FromQuery] string? deviceId,
             [FromQuery] int? activeWithinSeconds)
         {
             var result = _sessionManager.Sessions;
@@ -123,10 +123,10 @@ namespace Jellyfin.Api.Controllers
         [HttpPost("/Sessions/{sessionId}/Viewing")]
         [ProducesResponseType(StatusCodes.Status204NoContent)]
         public ActionResult DisplayContent(
-            [FromRoute] string sessionId,
-            [FromQuery] string itemType,
-            [FromQuery] string itemId,
-            [FromQuery] string itemName)
+            [FromRoute] string? sessionId,
+            [FromQuery] string? itemType,
+            [FromQuery] string? itemId,
+            [FromQuery] string? itemName)
         {
             var command = new BrowseRequest
             {
@@ -157,7 +157,7 @@ namespace Jellyfin.Api.Controllers
         [HttpPost("/Sessions/{sessionId}/Playing")]
         [ProducesResponseType(StatusCodes.Status204NoContent)]
         public ActionResult Play(
-            [FromRoute] string sessionId,
+            [FromRoute] string? sessionId,
             [FromQuery] Guid[] itemIds,
             [FromQuery] long? startPositionTicks,
             [FromQuery] PlayCommand playCommand,
@@ -191,7 +191,7 @@ namespace Jellyfin.Api.Controllers
         [HttpPost("/Sessions/{sessionId}/Playing/{command}")]
         [ProducesResponseType(StatusCodes.Status204NoContent)]
         public ActionResult SendPlaystateCommand(
-            [FromRoute] string sessionId,
+            [FromRoute] string? sessionId,
             [FromBody] PlaystateRequest playstateRequest)
         {
             _sessionManager.SendPlaystateCommand(
@@ -213,8 +213,8 @@ namespace Jellyfin.Api.Controllers
         [HttpPost("/Sessions/{sessionId}/System/{command}")]
         [ProducesResponseType(StatusCodes.Status204NoContent)]
         public ActionResult SendSystemCommand(
-            [FromRoute] string sessionId,
-            [FromRoute] string command)
+            [FromRoute] string? sessionId,
+            [FromRoute] string? command)
         {
             var name = command;
             if (Enum.TryParse(name, true, out GeneralCommandType commandType))
@@ -244,8 +244,8 @@ namespace Jellyfin.Api.Controllers
         [HttpPost("/Sessions/{sessionId}/Command/{Command}")]
         [ProducesResponseType(StatusCodes.Status204NoContent)]
         public ActionResult SendGeneralCommand(
-            [FromRoute] string sessionId,
-            [FromRoute] string command)
+            [FromRoute] string? sessionId,
+            [FromRoute] string? command)
         {
             var currentSession = RequestHelpers.GetSession(_sessionManager, _authContext, Request);
 
@@ -270,7 +270,7 @@ namespace Jellyfin.Api.Controllers
         [HttpPost("/Sessions/{sessionId}/Command")]
         [ProducesResponseType(StatusCodes.Status204NoContent)]
         public ActionResult SendFullGeneralCommand(
-            [FromRoute] string sessionId,
+            [FromRoute] string? sessionId,
             [FromBody, Required] GeneralCommand command)
         {
             var currentSession = RequestHelpers.GetSession(_sessionManager, _authContext, Request);
@@ -303,9 +303,9 @@ namespace Jellyfin.Api.Controllers
         [HttpPost("/Sessions/{sessionId}/Message")]
         [ProducesResponseType(StatusCodes.Status204NoContent)]
         public ActionResult SendMessageCommand(
-            [FromRoute] string sessionId,
-            [FromQuery] string text,
-            [FromQuery] string header,
+            [FromRoute] string? sessionId,
+            [FromQuery] string? text,
+            [FromQuery] string? header,
             [FromQuery] long? timeoutMs)
         {
             var command = new MessageCommand
@@ -330,7 +330,7 @@ namespace Jellyfin.Api.Controllers
         [HttpPost("/Sessions/{sessionId}/User/{userId}")]
         [ProducesResponseType(StatusCodes.Status204NoContent)]
         public ActionResult AddUserToSession(
-            [FromRoute] string sessionId,
+            [FromRoute] string? sessionId,
             [FromRoute] Guid userId)
         {
             _sessionManager.AddAdditionalUser(sessionId, userId);
@@ -347,7 +347,7 @@ namespace Jellyfin.Api.Controllers
         [HttpDelete("/Sessions/{sessionId}/User/{userId}")]
         [ProducesResponseType(StatusCodes.Status204NoContent)]
         public ActionResult RemoveUserFromSession(
-            [FromRoute] string sessionId,
+            [FromRoute] string? sessionId,
             [FromRoute] Guid userId)
         {
             _sessionManager.RemoveAdditionalUser(sessionId, userId);
@@ -368,9 +368,9 @@ namespace Jellyfin.Api.Controllers
         [HttpPost("/Sessions/Capabilities")]
         [ProducesResponseType(StatusCodes.Status204NoContent)]
         public ActionResult PostCapabilities(
-            [FromQuery] string id,
-            [FromQuery] string playableMediaTypes,
-            [FromQuery] string supportedCommands,
+            [FromQuery] string? id,
+            [FromQuery] string? playableMediaTypes,
+            [FromQuery] string? supportedCommands,
             [FromQuery] bool supportsMediaControl,
             [FromQuery] bool supportsSync,
             [FromQuery] bool supportsPersistentIdentifier = true)
@@ -401,7 +401,7 @@ namespace Jellyfin.Api.Controllers
         [HttpPost("/Sessions/Capabilities/Full")]
         [ProducesResponseType(StatusCodes.Status204NoContent)]
         public ActionResult PostFullCapabilities(
-            [FromQuery] string id,
+            [FromQuery] string? id,
             [FromBody, Required] ClientCapabilities capabilities)
         {
             if (string.IsNullOrWhiteSpace(id))
@@ -424,8 +424,8 @@ namespace Jellyfin.Api.Controllers
         [HttpPost("/Sessions/Viewing")]
         [ProducesResponseType(StatusCodes.Status204NoContent)]
         public ActionResult ReportViewing(
-            [FromQuery] string sessionId,
-            [FromQuery] string itemId)
+            [FromQuery] string? sessionId,
+            [FromQuery] string? itemId)
         {
             string session = RequestHelpers.GetSession(_sessionManager, _authContext, Request).Id;
 
diff --git a/Jellyfin.Api/Controllers/StartupController.cs b/Jellyfin.Api/Controllers/StartupController.cs
index d96b0f9934..cc1f797b13 100644
--- a/Jellyfin.Api/Controllers/StartupController.cs
+++ b/Jellyfin.Api/Controllers/StartupController.cs
@@ -75,9 +75,9 @@ namespace Jellyfin.Api.Controllers
         [HttpPost("Configuration")]
         [ProducesResponseType(StatusCodes.Status204NoContent)]
         public ActionResult UpdateInitialConfiguration(
-            [FromForm] string uiCulture,
-            [FromForm] string metadataCountryCode,
-            [FromForm] string preferredMetadataLanguage)
+            [FromForm] string? uiCulture,
+            [FromForm] string? metadataCountryCode,
+            [FromForm] string? preferredMetadataLanguage)
         {
             _config.Configuration.UICulture = uiCulture;
             _config.Configuration.MetadataCountryCode = metadataCountryCode;
diff --git a/Jellyfin.Api/Controllers/SubtitleController.cs b/Jellyfin.Api/Controllers/SubtitleController.cs
index 95cc39524c..baedafaa63 100644
--- a/Jellyfin.Api/Controllers/SubtitleController.cs
+++ b/Jellyfin.Api/Controllers/SubtitleController.cs
@@ -112,7 +112,7 @@ namespace Jellyfin.Api.Controllers
         [ProducesResponseType(StatusCodes.Status200OK)]
         public async Task<ActionResult<IEnumerable<RemoteSubtitleInfo>>> SearchRemoteSubtitles(
             [FromRoute] Guid itemId,
-            [FromRoute] string language,
+            [FromRoute] string? language,
             [FromQuery] bool? isPerfectMatch)
         {
             var video = (Video)_libraryManager.GetItemById(itemId);
@@ -132,7 +132,7 @@ namespace Jellyfin.Api.Controllers
         [ProducesResponseType(StatusCodes.Status204NoContent)]
         public async Task<ActionResult> DownloadRemoteSubtitles(
             [FromRoute] Guid itemId,
-            [FromRoute] string subtitleId)
+            [FromRoute] string? subtitleId)
         {
             var video = (Video)_libraryManager.GetItemById(itemId);
 
@@ -161,7 +161,7 @@ namespace Jellyfin.Api.Controllers
         [Authorize(Policy = Policies.DefaultAuthorization)]
         [ProducesResponseType(StatusCodes.Status200OK)]
         [Produces(MediaTypeNames.Application.Octet)]
-        public async Task<ActionResult> GetRemoteSubtitles([FromRoute] string id)
+        public async Task<ActionResult> GetRemoteSubtitles([FromRoute] string? id)
         {
             var result = await _subtitleManager.GetRemoteSubtitles(id, CancellationToken.None).ConfigureAwait(false);
 
@@ -186,9 +186,9 @@ namespace Jellyfin.Api.Controllers
         [ProducesResponseType(StatusCodes.Status200OK)]
         public async Task<ActionResult> GetSubtitle(
             [FromRoute, Required] Guid itemId,
-            [FromRoute, Required] string mediaSourceId,
+            [FromRoute, Required] string? mediaSourceId,
             [FromRoute, Required] int index,
-            [FromRoute, Required] string format,
+            [FromRoute, Required] string? format,
             [FromQuery] long? endPositionTicks,
             [FromQuery] bool copyTimestamps,
             [FromQuery] bool addVttTimeMap,
@@ -254,7 +254,7 @@ namespace Jellyfin.Api.Controllers
         public async Task<ActionResult> GetSubtitlePlaylist(
             [FromRoute] Guid itemId,
             [FromRoute] int index,
-            [FromRoute] string mediaSourceId,
+            [FromRoute] string? mediaSourceId,
             [FromQuery, Required] int segmentLength)
         {
             var item = (Video)_libraryManager.GetItemById(itemId);
@@ -324,7 +324,7 @@ namespace Jellyfin.Api.Controllers
         /// <returns>A <see cref="Task{Stream}"/> with the new subtitle file.</returns>
         private Task<Stream> EncodeSubtitles(
             Guid id,
-            string mediaSourceId,
+            string? mediaSourceId,
             int index,
             string format,
             long startPositionTicks,
diff --git a/Jellyfin.Api/Controllers/SystemController.cs b/Jellyfin.Api/Controllers/SystemController.cs
index e33821b248..bc606f7aad 100644
--- a/Jellyfin.Api/Controllers/SystemController.cs
+++ b/Jellyfin.Api/Controllers/SystemController.cs
@@ -193,7 +193,7 @@ namespace Jellyfin.Api.Controllers
         [HttpGet("Logs/Log")]
         [Authorize(Policy = Policies.RequiresElevation)]
         [ProducesResponseType(StatusCodes.Status200OK)]
-        public ActionResult GetLogFile([FromQuery, Required] string name)
+        public ActionResult GetLogFile([FromQuery, Required] string? name)
         {
             var file = _fileSystem.GetFiles(_appPaths.LogDirectoryPath)
                 .First(i => string.Equals(i.Name, name, StringComparison.OrdinalIgnoreCase));
diff --git a/Jellyfin.Api/Controllers/TvShowsController.cs b/Jellyfin.Api/Controllers/TvShowsController.cs
index 6738dd8c85..80b6a24883 100644
--- a/Jellyfin.Api/Controllers/TvShowsController.cs
+++ b/Jellyfin.Api/Controllers/TvShowsController.cs
@@ -190,7 +190,7 @@ namespace Jellyfin.Api.Controllers
         [ProducesResponseType(StatusCodes.Status200OK)]
         [ProducesResponseType(StatusCodes.Status404NotFound)]
         public ActionResult<QueryResult<BaseItemDto>> GetEpisodes(
-            [FromRoute] string seriesId,
+            [FromRoute] string? seriesId,
             [FromQuery] Guid userId,
             [FromQuery] string? fields,
             [FromQuery] int? season,
@@ -311,12 +311,12 @@ namespace Jellyfin.Api.Controllers
         [ProducesResponseType(StatusCodes.Status200OK)]
         [ProducesResponseType(StatusCodes.Status404NotFound)]
         public ActionResult<QueryResult<BaseItemDto>> GetSeasons(
-            [FromRoute] string seriesId,
+            [FromRoute] string? seriesId,
             [FromQuery] Guid userId,
-            [FromQuery] string fields,
+            [FromQuery] string? fields,
             [FromQuery] bool? isSpecialSeason,
             [FromQuery] bool? isMissing,
-            [FromQuery] string adjacentTo,
+            [FromQuery] string? adjacentTo,
             [FromQuery] bool? enableImages,
             [FromQuery] int? imageTypeLimit,
             [FromQuery] string? enableImageTypes,
diff --git a/Jellyfin.Api/Controllers/UserController.cs b/Jellyfin.Api/Controllers/UserController.cs
index 9f8d564a7d..24194dcc23 100644
--- a/Jellyfin.Api/Controllers/UserController.cs
+++ b/Jellyfin.Api/Controllers/UserController.cs
@@ -164,8 +164,8 @@ namespace Jellyfin.Api.Controllers
         [ProducesResponseType(StatusCodes.Status404NotFound)]
         public async Task<ActionResult<AuthenticationResult>> AuthenticateUser(
             [FromRoute, Required] Guid userId,
-            [FromQuery, BindRequired] string pw,
-            [FromQuery, BindRequired] string password)
+            [FromQuery, BindRequired] string? pw,
+            [FromQuery, BindRequired] string? password)
         {
             var user = _userManager.GetUserById(userId);
 
@@ -483,7 +483,7 @@ namespace Jellyfin.Api.Controllers
         /// <returns>A <see cref="Task"/> containing a <see cref="ForgotPasswordResult"/>.</returns>
         [HttpPost("ForgotPassword")]
         [ProducesResponseType(StatusCodes.Status200OK)]
-        public async Task<ActionResult<ForgotPasswordResult>> ForgotPassword([FromBody] string enteredUsername)
+        public async Task<ActionResult<ForgotPasswordResult>> ForgotPassword([FromBody] string? enteredUsername)
         {
             var isLocal = HttpContext.Connection.RemoteIpAddress.Equals(HttpContext.Connection.LocalIpAddress)
                           || _networkManager.IsInLocalNetwork(HttpContext.Connection.RemoteIpAddress.ToString());
@@ -501,7 +501,7 @@ namespace Jellyfin.Api.Controllers
         /// <returns>A <see cref="Task"/> containing a <see cref="PinRedeemResult"/>.</returns>
         [HttpPost("ForgotPassword/Pin")]
         [ProducesResponseType(StatusCodes.Status200OK)]
-        public async Task<ActionResult<PinRedeemResult>> ForgotPasswordPin([FromBody] string pin)
+        public async Task<ActionResult<PinRedeemResult>> ForgotPasswordPin([FromBody] string? pin)
         {
             var result = await _userManager.RedeemPasswordResetPin(pin).ConfigureAwait(false);
             return result;
diff --git a/Jellyfin.Api/Controllers/UserLibraryController.cs b/Jellyfin.Api/Controllers/UserLibraryController.cs
index 597e704693..ca804ebc95 100644
--- a/Jellyfin.Api/Controllers/UserLibraryController.cs
+++ b/Jellyfin.Api/Controllers/UserLibraryController.cs
@@ -265,12 +265,12 @@ namespace Jellyfin.Api.Controllers
         public ActionResult<IEnumerable<BaseItemDto>> GetLatestMedia(
             [FromRoute] Guid userId,
             [FromQuery] Guid parentId,
-            [FromQuery] string fields,
-            [FromQuery] string includeItemTypes,
+            [FromQuery] string? fields,
+            [FromQuery] string? includeItemTypes,
             [FromQuery] bool? isPlayed,
             [FromQuery] bool? enableImages,
             [FromQuery] int? imageTypeLimit,
-            [FromQuery] string enableImageTypes,
+            [FromQuery] string? enableImageTypes,
             [FromQuery] bool? enableUserData,
             [FromQuery] int limit = 20,
             [FromQuery] bool groupItems = true)
diff --git a/Jellyfin.Api/Controllers/UserViewsController.cs b/Jellyfin.Api/Controllers/UserViewsController.cs
index 38bf940876..ad8927262b 100644
--- a/Jellyfin.Api/Controllers/UserViewsController.cs
+++ b/Jellyfin.Api/Controllers/UserViewsController.cs
@@ -66,7 +66,7 @@ namespace Jellyfin.Api.Controllers
             [FromRoute] Guid userId,
             [FromQuery] bool? includeExternalContent,
             [FromQuery] bool includeHidden,
-            [FromQuery] string presetViews)
+            [FromQuery] string? presetViews)
         {
             var query = new UserViewQuery
             {
diff --git a/Jellyfin.Api/Controllers/VideoAttachmentsController.cs b/Jellyfin.Api/Controllers/VideoAttachmentsController.cs
index 943ba8af3d..eef0a93cdf 100644
--- a/Jellyfin.Api/Controllers/VideoAttachmentsController.cs
+++ b/Jellyfin.Api/Controllers/VideoAttachmentsController.cs
@@ -50,7 +50,7 @@ namespace Jellyfin.Api.Controllers
         [ProducesResponseType(StatusCodes.Status404NotFound)]
         public async Task<ActionResult<FileStreamResult>> GetAttachment(
             [FromRoute] Guid videoId,
-            [FromRoute] string mediaSourceId,
+            [FromRoute] string? mediaSourceId,
             [FromRoute] int index)
         {
             try
diff --git a/Jellyfin.Api/Controllers/VideosController.cs b/Jellyfin.Api/Controllers/VideosController.cs
index effe630a9b..fb1141984d 100644
--- a/Jellyfin.Api/Controllers/VideosController.cs
+++ b/Jellyfin.Api/Controllers/VideosController.cs
@@ -133,7 +133,7 @@ namespace Jellyfin.Api.Controllers
         [Authorize(Policy = Policies.RequiresElevation)]
         [ProducesResponseType(StatusCodes.Status204NoContent)]
         [ProducesResponseType(StatusCodes.Status400BadRequest)]
-        public ActionResult MergeVersions([FromQuery] string itemIds)
+        public ActionResult MergeVersions([FromQuery] string? itemIds)
         {
             var items = RequestHelpers.Split(itemIds, ',', true)
                 .Select(i => _libraryManager.GetItemById(i))
diff --git a/Jellyfin.Api/Controllers/YearsController.cs b/Jellyfin.Api/Controllers/YearsController.cs
index a036c818c9..a66a3951e1 100644
--- a/Jellyfin.Api/Controllers/YearsController.cs
+++ b/Jellyfin.Api/Controllers/YearsController.cs
@@ -64,16 +64,16 @@ namespace Jellyfin.Api.Controllers
         public ActionResult<QueryResult<BaseItemDto>> GetYears(
             [FromQuery] int? startIndex,
             [FromQuery] int? limit,
-            [FromQuery] string sortOrder,
-            [FromQuery] string parentId,
-            [FromQuery] string fields,
-            [FromQuery] string excludeItemTypes,
-            [FromQuery] string includeItemTypes,
-            [FromQuery] string mediaTypes,
-            [FromQuery] string sortBy,
+            [FromQuery] string? sortOrder,
+            [FromQuery] string? parentId,
+            [FromQuery] string? fields,
+            [FromQuery] string? excludeItemTypes,
+            [FromQuery] string? includeItemTypes,
+            [FromQuery] string? mediaTypes,
+            [FromQuery] string? sortBy,
             [FromQuery] bool? enableUserData,
             [FromQuery] int? imageTypeLimit,
-            [FromQuery] string enableImageTypes,
+            [FromQuery] string? enableImageTypes,
             [FromQuery] Guid userId,
             [FromQuery] bool recursive = true,
             [FromQuery] bool? enableImages = true)
diff --git a/Jellyfin.Api/Extensions/DtoExtensions.cs b/Jellyfin.Api/Extensions/DtoExtensions.cs
index ac248109d7..e61e9c29d9 100644
--- a/Jellyfin.Api/Extensions/DtoExtensions.cs
+++ b/Jellyfin.Api/Extensions/DtoExtensions.cs
@@ -23,7 +23,7 @@ namespace Jellyfin.Api.Extensions
         /// <param name="dtoOptions">DtoOptions object.</param>
         /// <param name="fields">Comma delimited string of fields.</param>
         /// <returns>Modified DtoOptions object.</returns>
-        internal static DtoOptions AddItemFields(this DtoOptions dtoOptions, string fields)
+        internal static DtoOptions AddItemFields(this DtoOptions dtoOptions, string? fields)
         {
             if (string.IsNullOrEmpty(fields))
             {
@@ -126,7 +126,7 @@ namespace Jellyfin.Api.Extensions
             bool? enableImages,
             bool? enableUserData,
             int? imageTypeLimit,
-            string enableImageTypes)
+            string? enableImageTypes)
         {
             dtoOptions.EnableImages = enableImages ?? true;
 
diff --git a/Jellyfin.Api/Helpers/RequestHelpers.cs b/Jellyfin.Api/Helpers/RequestHelpers.cs
index a8ba98f1f6..fd86feb8b1 100644
--- a/Jellyfin.Api/Helpers/RequestHelpers.cs
+++ b/Jellyfin.Api/Helpers/RequestHelpers.cs
@@ -20,7 +20,7 @@ namespace Jellyfin.Api.Helpers
         /// <param name="separator">The char that separates the substrings.</param>
         /// <param name="removeEmpty">Option to remove empty substrings from the array.</param>
         /// <returns>An array of the substrings.</returns>
-        internal static string[] Split(string value, char separator, bool removeEmpty)
+        internal static string[] Split(string? value, char separator, bool removeEmpty)
         {
             if (string.IsNullOrWhiteSpace(value))
             {
@@ -99,16 +99,14 @@ namespace Jellyfin.Api.Helpers
         /// <param name="sortBy">Sort by.</param>
         /// <param name="requestedSortOrder">Sort order.</param>
         /// <returns>Resulting order by.</returns>
-        internal static ValueTuple<string, SortOrder>[] GetOrderBy(string sortBy, string requestedSortOrder)
+        internal static ValueTuple<string, SortOrder>[] GetOrderBy(string? sortBy, string? requestedSortOrder)
         {
-            var val = sortBy;
-
-            if (string.IsNullOrEmpty(val))
+            if (string.IsNullOrEmpty(sortBy))
             {
                 return Array.Empty<ValueTuple<string, SortOrder>>();
             }
 
-            var vals = val.Split(',');
+            var vals = sortBy.Split(',');
             if (string.IsNullOrWhiteSpace(requestedSortOrder))
             {
                 requestedSortOrder = "Ascending";
diff --git a/Jellyfin.Api/Helpers/SimilarItemsHelper.cs b/Jellyfin.Api/Helpers/SimilarItemsHelper.cs
index 751e3c4815..fd0c315048 100644
--- a/Jellyfin.Api/Helpers/SimilarItemsHelper.cs
+++ b/Jellyfin.Api/Helpers/SimilarItemsHelper.cs
@@ -23,7 +23,7 @@ namespace Jellyfin.Api.Helpers
             IDtoService dtoService,
             Guid userId,
             string id,
-            string excludeArtistIds,
+            string? excludeArtistIds,
             int? limit,
             Type[] includeTypes,
             Func<BaseItem, List<PersonInfo>, List<PersonInfo>, BaseItem, int> getSimilarityScore)