langchain/llms/ai21.py/AI21/validate_environment
class AI21:    def validate_environment(cls, values: Dict) -> Dict:
        """Validate that api key exists in environment."""
        ai21_api_key = get_from_dict_or_env(values, "ai21_api_key", "AI21_API_KEY")
        values["ai21_api_key"] = ai21_api_key
        return values