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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_request_handler_chain(self, request_handler_chain):
 # type: (GenericRequestHandlerChain) -> None """Checks the type before adding it to the request_handler_chains instance variable. :param request_handler_chain: Request Handler Chain instance. :type request_handler_chain: RequestHandlerChain :raises: :py:class:`ask_sdk_runtime.exceptions.DispatchException` if a null input is provided or if the input is of invalid type """

        if request_handler_chain is None or not isinstance(
                request_handler_chain, GenericRequestHandlerChain):
            raise DispatchException(
                "Request Handler Chain is not a GenericRequestHandlerChain "
                "instance")
        self._request_handler_chains.append(request_handler_chain)