[FMX] check variable existence

Hi,

I have a frame where there a 5 input text fields that the user can fill in. THey may not fill them all in though. In the next frame I want to push the fields that they filled in into an array. My questions is how do I determine what they filled in and what they didn’t. Is there something like a if(isset(variable)){ do this } in Flash

I hope this makes sense.
-Mark