langchain/utilities/google_serper.py/GoogleSerperAPIWrapper/validate_environment
class GoogleSerperAPIWrapper:    def validate_environment(cls, values: Dict) -> Dict:
        """Validate that api key exists in environment."""
        serper_api_key = get_from_dict_or_env(
            values, "serper_api_key", "SERPER_API_KEY"
        )
        values["serper_api_key"] = serper_api_key

        return values