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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 content_length(self) -> Optional[int]: """The value of Content-Length HTTP header."""

        content_length = self._headers.get(hdrs.CONTENT_LENGTH)  # type: ignore

        if content_length is not None:
            return int(content_length)
        else:
            return None