def parse_url(url):
    """Return provider and project id
    >>> parse_url("github.com/user/repo")
    ('github.com', 'user/repo')
    >>> parse_url("bitbucket.org/user/repo")
    ('bitbucket.org', 'user/repo')
    >>> parse_url("gitlab.com/user/repo")
    ('gitlab.com', 'user/repo')
    >>> parse_url("A quick brown fox jumps over the lazy dog")
    (None, None)
    >>> parse_url(None)
    (None, None)
    """
    if url:
        url = url.split('://', 1)[-1]
        provider, rest = url.split('/', 1)
        if provider == 'sourceforge.net':
            return provider, rest.rsplit('/', 1)[-1]
        return provider, rest
    return None, None
