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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 get_file_size(self, fid):
 """ Gets size of uploaded file Or None if file doesn't exist. Args: **fid**: File identifier <volume_id>,<file_name_hash> Returns: Int or None """

        url = self.get_file_url(fid)
        res = self.conn.head(url)
        if res is not None:
            size = res.headers.get("content-length", None)
            if size is not None:
                return int(size)
        return None