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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 full_url(self):
 """Return the full reddit URL associated with the usernote. Arguments: subreddit: the subreddit name for the note (PRAW Subreddit object) """

        if self.link == '':
            return None
        else:
            return Note._expand_url(self.link, self.subreddit)