from typing import Optional


def get_key_from_response(response: dict) -> Optional[str]:
    """Return the s3 key to download, from the response to a list_objects_v2 call
    Returns None if no key found, otherwise arbitrarily picks first one listed.
    """
    keys = [contents['Key'] for contents in response.get('Contents', [])]
    if len(keys) == 0:
        return None
    else:
        return keys[0]