Update aws_lambda_powertools/utilities/data_classes/cognito_user_pool_event.py

Co-authored-by: Leandro Damascena <lcdama@amazon.pt>
Signed-off-by: Stéphane MENG <stephane.meng@gmail.com>

Author: knightmre

aws_lambda_powertools/utilities/data_classes/cognito_user_pool_event.py

@@ -549,8 +549,8 @@ def set_group_configuration_preferred_role(self, value: str):
 
 class TokenClaimsAndScopeOverrideDetails(DictWrapper):
     @property
-    def claims_to_add_or_override(self) -> Optional[Dict[str, str]]:
-        return self.get("claimsToAddOrOverride")
+    def claims_to_add_or_override(self) -> Dict[str, str]:
+        return self.get("claimsToAddOrOverride") or {}
 
     @claims_to_add_or_override.setter
     def claims_to_add_or_override(self, value: Dict[str, str]):