[Form] Let null values to unset fields in PATCH requests

src/Symfony/Component/Form/Form.php

@@ -548,7 +548,7 @@ class Form implements \IteratorAggregate, FormInterface
                 }
 
                 foreach ($this->children as $name => $child) {
-                    if (isset($submittedData[$name]) || $clearMissing) {
+                    if (array_key_exists($name, $submittedData) || $clearMissing) {
                         $child->submit(isset($submittedData[$name]) ? $submittedData[$name] : null, $clearMissing);
                         unset($submittedData[$name]);
                     }

src/Symfony/Component/Form/Tests/CompoundFormTest.php

@@ -82,6 +82,19 @@ class CompoundFormTest extends AbstractFormTest
         $this->assertTrue($form->isValid());
     }
 
+    public function testSubmitForwardsNullIfNotClearMissingButValueIsExplicitlyNull()
+    {
+        $child = $this->getMockForm('firstName');
+
+        $this->form->add($child);
+
+        $child->expects($this->once())
+            ->method('submit')
+            ->with($this->equalTo(null));
+
+        $this->form->submit(array('firstName' => null), false);
+    }
+
     public function testSubmitForwardsNullIfValueIsMissing()
     {
         $child = $this->getMockForm('firstName');