code: def add_request_handler_chain(self, request_handler_chain):
          # type: (GenericRequestHandlerChain) -> None
          
          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)
docs: 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