[Form][2.7][ Choice type] fixed groups with empty array.

src/Symfony/Component/Form/ChoiceList/Factory/DefaultChoiceListFactory.php

@@ -172,6 +172,10 @@ class DefaultChoiceListFactory implements ChoiceListFactoryInterface
     private static function addChoiceViewsGroupedBy($groupBy, $label, $choices, $keys, &$index, $attr, $isPreferred, &$preferredViews, &$otherViews)
     {
         foreach ($groupBy as $key => $value) {
+            if (null === $value) {
+                continue;
+            }
+
             // Add the contents of groups to new ChoiceGroupView instances
             if (is_array($value)) {
                 $preferredViewsForGroup = array();

src/Symfony/Component/Form/Tests/ChoiceList/Factory/DefaultChoiceListFactoryTest.php

@@ -536,6 +536,7 @@ class DefaultChoiceListFactoryTest extends \PHPUnit_Framework_TestCase
         $list = new ArrayChoiceList(array(
             'Group 1' => array('A' => $this->obj1, 'B' => $this->obj2),
             'Group 2' => array('C' => $this->obj3, 'D' => $this->obj4),
+            'Group empty' => array(),
         ));
 
         $view = $this->factory->createView(