title: Multi select dropdown CakePHP 3 selected issue
body: <pre><code>$selected_country = array(1,3);
  
  $this-&gt;Form-&gt;input('country', [
      'options' =&gt; $source_types,
      'label' =&gt; 'Country: ',
      'multiple' =&gt; true,
      'class' =&gt; ' form-control',
      'selected' =&gt; $selected_country,
      'type' =&gt; 'select'
  ]);
  </code></pre>
  
  <p>If selected country has only one value then it selects the option but if the selected country has more than one value then it doesn't select any value.</p>