title: how to make form ignore password fields if blank (symfony2 forms)
body: <p>I have a simple user manager in my backend, and I want to be able to edit the user without setting a new password/repeating the old password every time.</p>
  
  <p>Right now if I leave the password fields blank when editing a user, symfony2 complains that a password must be entered, and of course I want this functionality when I register new users, but when I edit them, I'd like for the form to just ignore the password boxes if they aren't filled out.</p>
  
  <p>How is this accomplished?</p>