Fix to allow null values in labels array

src/Symfony/Component/Form/Extension/Core/ChoiceList/ChoiceList.php

@@ -261,7 +261,7 @@ class ChoiceList implements ChoiceListInterface
     {
         // Add choices to the nested buckets
         foreach ($choices as $group => $choice) {
-            if (!isset($labels[$group])) {
+            if (!array_key_exists($group, $labels)) {
                 throw new \InvalidArgumentException('The structures of the choices and labels array do not match.');
             }
 

src/Symfony/Component/Form/Tests/Extension/Core/ChoiceList/ChoiceListTest.php

@@ -184,4 +184,20 @@ class ChoiceListTest extends \PHPUnit_Framework_TestCase
             array('A')
         );
     }
+
+    /**
+     * test for pull request: https://github.com/symfony/symfony/pull/5394
+     */
+    public function testLabelsContainingNull()
+    {
+        $this->list = new ChoiceList(
+            array($this->obj1, $this->obj2),
+            array('A', null)
+        );
+
+        $this->assertEquals(
+            array(0 => new ChoiceView($this->obj1, '0', 'A'), 1 => new ChoiceView($this->obj2, '1', null)),
+            $this->list->getRemainingViews()
+        );
+    }
 }