title: SonataAdminBundle can not update the user password
body: <p>I can not update the user password via sonataadmin dashboard.</p>
  
  <p>I use symfony2 FosUserBundle2.0  SonataAdminBundle(but <strong>not</strong> use SonataUserBundle) and follow the Document to do.</p>
  
  <p><code>MyUserBundle\Admin\UserAdmin.php</code> class UserAdmin extends Admin like this</p>
  
  <pre><code>protected function configureFormFields(FormMapper $formMapper)
  {
      $formMapper
          ......
          -&gt;add('plainPassword', 'repeated', array(
              'type' =&gt; 'password',
              'options' =&gt; array('translation_domain' =&gt; 'FOSUserBundle'),
              'first_options' =&gt; array('label' =&gt; 'form.password'),
              'second_options' =&gt; array('label' =&gt; 'form.password_confirmation'),
              'invalid_message' =&gt; 'fos_user.password.mismatch',
                  'required'    =&gt; false,
              )
          )
          ..
  }
  </code></pre>
  
  <p>there is no problem when i use <code>sonataadminbundle</code> dashboard to create a new user, but when i use dashboard to update the password,the password in DB doesn't change.</p>
  
  <p>the others can update but the password, i don't know why. there is no any errror message.</p>
  
  <p>I am new in symfony2, some one help me?</p>
  
  <p><strong>thanks to kwozny ,now i fix it~</strong>
  i don't change the function configureFormFields code, just follow kwozny's advise , add the following code.i don't know why ,but i works!
  i can update the password and when i update the others(password field is empty) the password will not change. </p>
  
  <pre><code>public function prePersist($object)
      {
          parent::prePersist($object);
  
      }
      public function preUpdate($object)
      {
          parent::preUpdate($object);
  
      }
  </code></pre>