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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 link_exceptions(self, custom_exception=None, dashi_exception=None):
 """Link a custom exception thrown on the receiver to a dashi exception """

        if custom_exception is None:
            raise ValueError("custom_exception must be set")
        if dashi_exception is None:
            raise ValueError("dashi_exception must be set")

        self._linked_exceptions[custom_exception] = dashi_exception