FilterBox,BigNumber,WorldMap: Handle empty results - second attempt (#9789)

* FilteBox: handle empty results (second attempt)

This change was originally attempted in #9671 but reverted
since it broke FilterBox charts with only a time selector.

After some tests I reworked the patch to avoid returning None,
but instead returning an empty list for each col/selector with
an empty dataframe associated. This allows to see all the selectors
without any breakage.

* BigNumberViz: avoid user facing errors when the dataframe is empty

* WorldMapViz: avoid user facing errors when the dataframe is empty

superset/viz.py

@@ -1133,6 +1133,9 @@ class BigNumberViz(BaseViz):
         return d
 
     def get_data(self, df: pd.DataFrame) -> VizData:
+        if df.empty:
+            return None
+
         df = df.pivot_table(
             index=DTTM_ALIAS,
             columns=[],
@@ -1868,6 +1871,9 @@ class WorldMapViz(BaseViz):
         return qry
 
     def get_data(self, df: pd.DataFrame) -> VizData:
+        if df.empty:
+            return None
+
         from superset.examples import countries
 
         fd = self.form_data
@@ -1942,7 +1948,7 @@ class FilterBoxViz(BaseViz):
             col = flt.get("column")
             metric = flt.get("metric")
             df = self.dataframes.get(col)
-            if df is not None:
+            if df is not None and not df.empty:
                 if metric:
                     df = df.sort_values(
                         utils.get_metric_name(metric), ascending=flt.get("asc")
@@ -1957,6 +1963,8 @@ class FilterBoxViz(BaseViz):
                         {"id": row[0], "text": row[0]}
                         for row in df.itertuples(index=False)
                     ]
+            else:
+                df[col] = []
         return d