How do you Make a Notifer Make a Message When a ListPicker is Left Empty?

Hello, everyone. I was in MIT App Inventor, trying to make a Notifer tell the user that they should pick something when a Listpicker is Left Empty. I am having trouble doing so. Can someone help me? This is the Code I did so far.

Screenshot 2024-05-04 9.44.15 AM

Like so:


Best thing to do is to make the listpicker button invisible, and use another button to call the listpicker

or like this once the listpicker becomes empty: