title: Symfony getData event subscriber is null
body: <p>I know this question has been asked already a couple of times, but there hasn't been an answer that actually helped me solving my problem.</p>
  
  <p>I've got three EventSubscribers for three Dropdowns who are dependent on each other.</p>
  
  <p>So in my FormType I say:</p>
  
  <pre><code>  public function buildForm(FormBuilderInterface $builder, array $options)
  {
    // solution showmethecode
    $pathToAgencies = 'agencies';
    //
    $builder
      -&gt;addEventSubscriber(new AddChannel1Subscriber($pathToAgencies))
      -&gt;addEventSubscriber(new AddChannel3Subscriber($pathToAgencies))
      -&gt;addEventSubscriber(new AddAgencySubscriber($pathToAgencies));
  
  }
  </code></pre>
  
  <p>and one of my EventSubscribers looks like that:</p>
  
  <pre><code>    ...
  ...
  
          public static function getSubscribedEvents() {
              return array(
                FormEvents::PRE_SET_DATA  =&gt; 'preSetData',
                FormEvents::PRE_SUBMIT    =&gt; 'preSubmit'
              );
            }
  
            private function addChannel1Form($form, $channel1s = null) {
              $formOptions = array(
                'class' =&gt; 'AppBundle:Channel1',
                  'property' =&gt; 'name',
                  'label' =&gt; 'label.channel1s',
                  'empty_value' =&gt; 'label.select_channel1s',
                  'mapped' =&gt; false,
                  'expanded' =&gt; false,
                  'translation_domain' =&gt; 'UploadProfile',
                  'multiple' =&gt; true,
                  'required' =&gt; false,
                  'attr' =&gt; array(
                    'class' =&gt; 'channel1s'
                  ),
              );
  
              if ($channel1s){
                $formOptions['data'] = $channel1s;
              }
              $form-&gt;add('channel1s', 'entity', $formOptions);
            }
  
            public function preSetData(FormEvent $event) {
              $data = $event-&gt;getData();
              $form = $event-&gt;getForm();
  
                  if (null === $data) {
                      return;
                  }
  
              $accessor = PropertyAccess::createPropertyAccessor();
              $agency = $accessor-&gt;getValue($data, $this-&gt;pathToAgency);
              $channel1s = ($agency) ? $agency-&gt;getChannel3s()-&gt;getChannel1s() : null;
              $this-&gt;addChannel1Form($form, $channel1s);
            }
  
            public function preSubmit(FormEvent $event) {
              $form = $event-&gt;getForm();
              $this-&gt;addChannel1Form($form);
            }
      ...
  </code></pre>
  
  <p>Now I'm getting the error "Attempted to call an undefined method named "getChannel3s" of class "Doctrine\Common\Collections\ArrayCollection"." and (I think) this is because my <code>$data</code> in my preSetData is NULL but I don't know why it's null. Am I looking at the wrong spot or where is my mistake here?</p>