bug symfony#10251 [Form][2.3] Fixes empty file-inputs getting treated as extra field. (jenkoian)

This PR was squashed before being merged into the 2.3 branch (closes symfony#10251).

Discussion
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[Form][2.3] Fixes empty file-inputs getting treated as extra field.

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | symfony#8575 (symfony#8575 (comment))
| License       | MIT

Re-applies 968fe23 (PR symfony#8575).

The test for this already exists, it was just this line that got overwritten by symfony@eb9f76d#diff-ca5e25b47f3ecc94cd557946aeb486c6L542

To clarify, this is a PR into 2.3 branch - this already exists in 2.4 (and later from this PR: symfony#9146)

Commits
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8d99d75 [Form][2.3] Fixes empty file-inputs getting treated as extra field.

Author: fabpot

src/Symfony/Component/Form/Form.php

@@ -556,7 +556,7 @@ public function submit($submittedData, $clearMissing = true)
                 }
 
                 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

@@ -115,7 +115,7 @@ public function testSubmitDoesNotAddExtraFieldForNullValues()
         $child = $factory->create('file', null, array('auto_initialize' => false));
 
         $this->form->add($child);
-        $this->form->submit(array('file' => null));
+        $this->form->submit(array('file' => null), false);
 
         $this->assertCount(0, $this->form->getExtraData());
     }