help with checking a variable is not empty

In the tutorial (I'm using SL 2) for interactivity https://youtu.be/PWAN2zRM2W0?t=392 there is a text variable entry (yourname). You click submit and the trigger sends you to the next slide. 

I would like to have a trigger that checks to make sure the user did not click submit without entering a name. I tried Show layer (with a feedback saying "fill in the box") when the user clicks the submit button If yourname is = to blank. That doesn't work. 

I tried putting in a hotspot that shows the layer. That works to show the layer and I put a trigger to hide the layer when user clicks on the text entry box. However, then the submit button doesn't work. When I send the hotspot to the back, the button gets the click and it goes to the next slide even if the text box is empty. 

What to do? Thanks, Steve