langchain/document_loaders/github.py/BaseGitHubLoader/validate_environment
class BaseGitHubLoader:    def validate_environment(cls, values: Dict) -> Dict:
        """Validate that access token exists in environment."""
        values["access_token"] = get_from_dict_or_env(
            values, "access_token", "GITHUB_PERSONAL_ACCESS_TOKEN"
        )
        return values