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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 _exec_command(self, cmd):
 """Run a command on the remote SSH server. Returns: bytes: the output of the command, if it didn't fail None: if the error pipe of the command was not empty """

        _, out, err = self._client.exec_command(cmd, timeout=self._timeout)
        return out.read().strip() if not err.read().strip() else None