hello all RSform users

i have a 2 rsform that my user can upload a file as personality Picture with a upload component and onother textbox field
and i insert address of uploaded file in mytable .
ok until this.
but when user want to change another text box field and not selected any file to upload my addres file field in database is emty or({upload:path})
my question is how to control my update form if user not selected any file,so i dont want to change my addres file field in database but i want to change another textbox field

for example this is updated form mapping: i have two rsform:one for insert and another for Update that toghethr is same this:

name:________
Email:_______
Phone:_______
Picture:________Brows...

please help me...