minor #13848 Update direct_submit.rst (KamilKubicki)

This PR was submitted for the 5.1 branch but it was merged into the 4.4 branch instead.

Discussion
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Update direct_submit.rst

Missing variable initialisation used in createForm function.

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Commits
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4483d0a Update direct_submit.rst

Author: javiereguiluz

form/direct_submit.rst

@@ -15,6 +15,7 @@ control over when exactly your form is submitted and what data is passed to it::
 
     public function new(Request $request)
     {
+        $task = new Task();
         $form = $this->createForm(TaskType::class, $task);
 
         if ($request->isMethod('POST')) {