title: Symfony Sonata project: How to add multiple input texts to block?
body: <p>I would like to add a collection of input text with same name (i.e. name="blabla[]") filed to admin <strong>block</strong> with add/delete buttons.</p>
  
  <p>I'm using <code>collection</code> form field type but can't see add/delete buttons</p>
  
  <pre><code>public function buildEditForm(FormMapper $formMapper, BlockInterface $block)
  {
      $formMapper-&gt;add('settings', 'sonata_type_immutable_array', array(
          'keys' =&gt; array(
              array('title', 'collection', 
                  array('type' =&gt; 'text' ,
                      'required' =&gt; true,
                      'allow_add' =&gt; true,
                      'data' =&gt; array('First' =&gt; 'One')
                      )
                  )
          )
      ));
  }
  </code></pre>
  
  <p>I get below result without add/delete buttons!
  <a href="https://i.stack.imgur.com/t3ESr.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/t3ESr.png" alt="enter image description here"></a></p>
  
  <p>Any idea how to get it working ?</p>