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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 output_dict(self):
 """Get dictionary representation of output arrays. Returns ------- output_dict : dict of str to NDArray The dictionary that maps name of output names to NDArrays. Raises ------ ValueError : if there are duplicated names in the outputs. """

        if self._output_dict is None:
            self._output_dict = Executor._get_dict(
                self._symbol.list_outputs(), self.outputs)
        return self._output_dict