Fix mypy type errors in flag dependencies

- Add type validation for flag dependency expected values
- Handle Optional[bool] returns from match_flag_property correctly
- Use explicit variable assignments to satisfy mypy type checker

This resolves type checking issues while maintaining functionality.

Author: haacked

posthog/feature_flags.py

@@ -441,6 +441,13 @@ def match_flag_property(
 
     if not dependency_id:
         return None
+    
+    # Validate expected_value type
+    if not isinstance(expected_value, (bool, str)):
+        log.warning(
+            f"Invalid value type for flag dependency: {type(expected_value)}. Expected bool or str."
+        )
+        return None
 
     # Only exact operator is supported for flag dependencies
     if operator != "exact":
@@ -578,15 +585,16 @@ def is_condition_match(
                     prop, properties, cohort_properties, dependency_graph, id_to_key
                 )
             elif property_type == "flag":
-                matches = match_flag_property(prop, dependency_graph, id_to_key)
-                if matches is None:
+                flag_matches = match_flag_property(prop, dependency_graph, id_to_key)
+                if flag_matches is None:
                     # Dependency not available, skip this condition
                     log.warning(
                         "Flag dependency on '%s' not available for flag '%s'. Skipping condition.",
                         prop.get("key", "unknown"),
                         feature_flag.get("key", "unknown"),
                     )
                     continue
+                matches = flag_matches
             else:
                 matches = match_property(prop, properties)
             if not matches:
@@ -818,14 +826,15 @@ def match_property_group(
                         id_to_key,
                     )
                 elif prop.get("type") == "flag":
-                    matches = match_flag_property(prop, dependency_graph, id_to_key)
-                    if matches is None:
+                    flag_matches = match_flag_property(prop, dependency_graph, id_to_key)
+                    if flag_matches is None:
                         # Dependency not available, skip this condition
                         log.warning(
                             "Flag dependency on '%s' not available. Skipping condition.",
                             prop.get("key", "unknown"),
                         )
                         continue
+                    matches = flag_matches
                 else:
                     matches = match_property(prop, property_values)