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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:
 async def preprocess_request( self, request_context: Optional[RequestContext]=None, ) -> Optional[ResponseReturnValue]: """Preprocess the request i.e. call before_request functions. Arguments: request_context: The request context, optional as Flask omits this argument. """

        request_ = (request_context or _request_ctx_stack.top).request
        blueprint = request_.blueprint
        processors = self.url_value_preprocessors[None]
        if blueprint is not None:
            processors = chain(processors, self.url_value_preprocessors[blueprint])  # type: ignore
        for processor in processors:
            processor(request.endpoint, request.view_args)

        functions = self.before_request_funcs[None]
        if blueprint is not None:
            functions = chain(functions, self.before_request_funcs[blueprint])  # type: ignore
        for function in functions:
            result = await function()
            if result is not None:
                return result
        return None