def is_github_url(url):
    """Tell if a given URL matches a Github one.

    Args:
        url (str): The URL to test. It can be None.

    Returns:
        bool: False if the URL is not a string or if it doesn't match a Github URL

    """
    if isinstance(url, str):
        return url.startswith('https://github.com/') or url.startswith(
            'ssh://github.com/')
    else:
        return False
