Check whether People Picker field is empty

Dear all, I have a problem to check whether a people picker field is empty or not since I want to make a custom validation with javascript function. I can not set this field as required field since I want this is field is required only when some conditions are applied. I tried to put alert on every condition in the javascript function and I get a fact that if (NWF$.trim(commentText) == "") just doesn’t work with people picker type. I have attached my form so it can be reviewed. Thank you very much for your help!