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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _validate(url):
 """Validate a url. :param str url: Polling URL extracted from response header. :raises: ValueError if URL has no scheme or host. """

    if url is None:
        return
    parsed = urlparse(url)
    if not parsed.scheme or not parsed.netloc:
        raise ValueError("Invalid URL header")