langchain/document_loaders/github.py/GitHubIssuesLoader/validate_since
class GitHubIssuesLoader:    def validate_since(cls, v: Optional[str]) -> Optional[str]:
        if v:
            try:
                datetime.strptime(v, "%Y-%m-%dT%H:%M:%SZ")
            except ValueError:
                raise ValueError(
                    "Invalid value for 'since'. Expected a date string in "
                    f"YYYY-MM-DDTHH:MM:SSZ format. Received: {v}"
                )
        return v