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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 url(self):
 """ Returns the URL to this record. Returns None if not known """

        if self.server_url is not None and \
                self.recid is not None:
            return '/'.join(
                [self.server_url, CFG_SITE_RECORD, str(self.recid)])
        else:
            return None