Strip whitespace characters from the beginning and the end of the url
    and add a default scheme.

def fix_url(url):
    """
    Strip whitespace characters from the beginning and the end of the url
    and add a default scheme.
    """
    if url is None:
        return None

    url = url.strip()

    if url and not urlparse(url).scheme:
        url = "http://" + url

    return url