Conditions on text variables

Hi, community!

I have created a course where the opening slide has a text variable for the user to enter their name. When they hit SUBMIT, they are taken to the next slide where their name appears and they crack on with the course. 

I am hoping to get some help as to how I would set it up so that if the user tries to hit the SUBMIT button without typing in their name in the text entry field that a layer pops up saying something like "Awww, please tell us your name" and then they return to the main text variable slide. 

I can't seem to figure out what triggers I would need to have set up and where in order for this to work.

I have attached images of my main slide and layer with the triggers I have currently set up (hoping that is of some use!)

Thanks in advance, 

Karyn