Incorrect/invalid select tag is generated if choices have duplicate content ('Category 4'). ``` php $f = $this->formFactory->createNamedBuilder('category', 'form') ->add('parent_category', 'choice', array( 'label' => 'Name', 'choices' => array( '1' => 'Category 1', '2' => 'Category 4', '3' => 'Category 3', '4' => 'Category 4', '5' => 'Category 5' ) )) ->add('save', 'submit', array( 'label' => 'Save' )) ->getForm(); ``` ``` html <select> <option value="1" >Category 1</option> <option value="4" >Category 4</option> <option value="3" >Category 3</option> <option value="5" >Category 5</option> </select> ``` Where is option with value="2"?