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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 add_output(self, output):
 """Adds an output to a Transaction's list of outputs. Args: output (:class:`~bigchaindb.common.transaction. Output`):
 An Output to be added to the Transaction. """

        if not isinstance(output, Output):
            raise TypeError('`output` must be an Output instance or None')
        self.outputs.append(output)