Hiding Action Button Until Content Entered in a Table

I would like to use Desmos to have students complete a two-column proof. I would like to allow the students the opportunity to check their work after completing each row of a proof. I am unsure how to code the Action Button to check the table for “not empty”. I have used action buttons with tables before, but the only coding source I can find for this is cellNumericValue, but I want to allow for other content besides just numbers. Thanks

Here is an example of the activity I am trying to create:

There is also cellContent, which should do the trick.

So something like not(isBlank(cellContent(..., ...))) will return true once there’s a value in there, or false otherwise.

Thanks so much for your help. Here is the coding that I am trying, but it isn’t working for me. Can you please help me decipher where I am making my mistake?

hidden: not(isBlank.Proof1.cellContent (1.1))

hidden: not(isBlank(Proof1.cellContent(1,1)))

The coding for this worked, but it’s still not quite what I am looking for. I want it a component to be hidden up until the cell is not blank. Right now, the component shows until someone types in the cell and then it disappears.

So hidden: isBlank(Proof1.cellContent(1,1))