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