title: ActiveAdmin: how to leave user password unchanged?
body: <p>I am using ActiveAdmin as my administration backend in my rails app. Basically, I have an <code>admin_user</code> and a <code>user</code> model.  </p>
  
  <p>When I create a new user from an admin account, I specify an email and a password, that is ok.  </p>
  
  <p>Let's say I then want to modify the user's email but not the password... it seems this cannot be done as the password field cannot be blank when updating a user.  </p>
  
  <p>Is there a configuration somewhere that would consider that the password is unchanged is the fields (password and password_confirmation) are left blank while updating a user?</p>