feature drift reduce output method fix (#2428)

deepchecks/tabular/checks/train_test_validation/feature_drift.py

@@ -282,7 +282,7 @@ def run_logic(self, context: Context) -> CheckResult:
     def reduce_output(self, check_result: CheckResult) -> Dict[str, float]:
         """Return an aggregated drift score based on aggregation method defined."""
         feature_importance = pd.Series({column: info['Importance'] for column, info in check_result.value.items()})
-        feature_importance = None if None in feature_importance else feature_importance
+        feature_importance = None if None in feature_importance.values else feature_importance
         values = pd.Series({column: info['Drift score'] for column, info in check_result.value.items()})
         return self.feature_reduce(self.aggregation_method, values, feature_importance, 'Drift Score')