Flash/PHP E-mail form sending blank e-mails

Hello everyone! I have done Senocular’s tutorial “Flash-Based Email Form Using PHP” and find one small problem. The form sends a blank e-mail if there is nothing written on the textfields and the user presses “send”. How could I prevent this? What I want my form to do is if user presses the “send” button and the text fields are empty, my flash goes to a frame where it tells the user to fill all the textfields. Anyone know a solution for this? Thanks in advance. -sumo-