[PropertyInfo] ReflectionExtractor: give a chance to other extractors if no properties

src/Symfony/Component/PropertyInfo/Extractor/ReflectionExtractor.php

@@ -76,7 +76,7 @@ class ReflectionExtractor implements PropertyListExtractorInterface, PropertyTyp
             $properties[$propertyName] = $propertyName;
         }
 
-        return array_values($properties);
+        return $properties ? array_values($properties) : null;
     }
 
     /**

src/Symfony/Component/PropertyInfo/Tests/Extractors/ReflectionExtractorTest.php

@@ -57,6 +57,8 @@ class ReflectionExtractorTest extends TestCase
             ),
             $this->extractor->getProperties('Symfony\Component\PropertyInfo\Tests\Fixtures\Dummy')
         );
+
+        $this->assertNull($this->extractor->getProperties('Symfony\Component\PropertyInfo\Tests\Fixtures\NoProperties'));
     }
 
     /**

src/Symfony/Component/PropertyInfo/Tests/Fixtures/NoProperties.php

@@ -0,0 +1,21 @@
+<?php
+
+namespace Symfony\Component\PropertyInfo\Tests\Fixtures;
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\PropertyInfo\Tests\Fixtures;
+
+/**
+ * @author Kévin Dunglas <dunglas@gmail.com>
+ */
+class NoProperties
+{
+}