[mypy] Enforcing typing for superset.utils (#9905)

Co-authored-by: John Bodley <john.bodley@airbnb.com>

superset/utils/feature_flag_manager.py

@@ -15,25 +15,33 @@
 # specific language governing permissions and limitations
 # under the License.
 from copy import deepcopy
+from typing import Any, Dict
+
+from flask import Flask
 
 
 class FeatureFlagManager:
     def __init__(self) -> None:
         super().__init__()
         self._get_feature_flags_func = None
-        self._feature_flags = None
+        self._feature_flags: Dict[str, Any] = {}
 
-    def init_app(self, app):
-        self._get_feature_flags_func = app.config.get("GET_FEATURE_FLAGS_FUNC")
-        self._feature_flags = app.config.get("DEFAULT_FEATURE_FLAGS") or {}
-        self._feature_flags.update(app.config.get("FEATURE_FLAGS") or {})
+    def init_app(self, app: Flask) -> None:
+        self._get_feature_flags_func = app.config["GET_FEATURE_FLAGS_FUNC"]
+        self._feature_flags = app.config["DEFAULT_FEATURE_FLAGS"]
+        self._feature_flags.update(app.config["FEATURE_FLAGS"])
 
-    def get_feature_flags(self):
+    def get_feature_flags(self) -> Dict[str, Any]:
         if self._get_feature_flags_func:
             return self._get_feature_flags_func(deepcopy(self._feature_flags))
 
         return self._feature_flags
 
-    def is_feature_enabled(self, feature) -> bool:
+    def is_feature_enabled(self, feature: str) -> bool:
         """Utility function for checking whether a feature is turned on"""
-        return self.get_feature_flags().get(feature)
+        feature_flags = self.get_feature_flags()
+
+        if feature_flags and feature in feature_flags:
+            return feature_flags[feature]
+
+        return False