title: Set easyadmin_autocomplete Select Null by default. Symfony
body: <p>I would like to know if there is any way to put <code>null</code> value by <em>default</em> in the <em>easyadmin_autocomplete select</em>.</p>
  
  <p>The first item in the list is selected and filled with data from database but i need a <code>null</code> value by default and setted automaticly. The goal is a first result point to an empty one (Choose one...).</p>
  
  <p>Do you know how to do it?</p>
  
  <p>Can you think of any way combining the options defined below?</p>
  
  <pre><code>#easy_admin.yml
  Product:
        class: App\Entity\Product
        controller: App\Controller\ProductController
        new:
          fields:
            - { property: 'category', label: 'Category', type: 'easyadmin_autocomplete', type_options: { class: 'App\Entity\Category' } }
   }
  
  </code></pre>
  
  <p>In this example, one select has a <code>placeholder</code> with the text 'Any' (Ninguno). I need to know why is handling them different.
  <a href="https://i.stack.imgur.com/IwQ48.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/IwQ48.png" alt="form_pic"></a>
  These are the options defined for the attr <em>fields -> type_options</em> of the <code>yml</code>:</p>
  
  <ol>
  <li>action</li>
  <li>allow_extra_fields</li>
  <li>allow_file_upload</li>
  <li>attr</li>
  <li>auto_initialize</li>
  <li>block_name</li>
  <li>by_reference</li>
  <li>class</li>
  <li>compound</li>
  <li>constraints</li>
  <li>csrf_field_name</li>
  <li>csrf_message</li>
  <li>csrf_protection</li>
  <li>csrf_token_id</li>
  <li>csrf_token_manager</li>
  <li>data</li>
  <li>data_class</li>
  <li>disabled</li>
  <li>empty_data</li>
  <li>error_bubbling</li>
  <li>error_mapping</li>
  <li>extra_fields_message</li>
  <li>help</li>
  <li>help_attr</li>
  <li>inherit_data</li>
  <li>invalid_message</li>
  <li>invalid_message_parameters</li>
  <li>label</li>
  <li>label_attr</li>
  <li>label_format</li>
  <li>mapped</li>
  <li>method</li>
  <li>multiple</li>
  <li>post_max_size_message</li>
  <li>property_path</li>
  <li>required</li>
  <li>translation_domain</li>
  <li>trim</li>
  <li>upload_max_size_message</li>
  <li>validation_groups</li>
  </ol>