Execute a rule on received update MQTT

Is there a way to have a rule like the following only execute when a blank message is received on a topic of MQTT? I have a device that requests info and i can get the info to it easily through just updating an item that pushes a message on a MQTT topic when updated, but the request message is blank.

At the moment i’v tried the basic Item monitor1 received update but that only works when the request message has a value inside, but it doesn’t so is there a way to execute my command on a blank message trigger?