code: def require_response_keys(
      responses: List[Dict[Text, Any]], _: Dict, __: Text
  ) -> Union[SchemaError, bool]:
      """Validates that response dicts have either the "text" key or the "custom" key."""
      for response in responses:
          if not isinstance(response, dict):
              # this is handled by other validation rules
              continue
  
          if response.get("text") is None and not response.get(
              "custom"
          ):
              return SchemaError(
                  "Missing 'text' or 'custom' key in response or "
                  "null 'text' value in response."
              )
  
      return True
  
label_desc: Use image node_id 1 for calling a global function with example usage: require_response_keys(responses, _, __) and returns: True, SchemaError