bug symfony#6800 Fix missing function name (JosefVitu)

This PR was merged into the 2.7 branch.

Discussion
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Fix missing function name

Example in the 'Handling Form Submissions' section was invalid, as the name of a function to be called (isValid) was missing.

Commits
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6ed019e Fix missing function name

Author: wouterj

forms.rst

@@ -234,7 +234,7 @@ your controller::
 
         $form->handleRequest($request);
 
-        if ($form->isSubmitted() && $form->()) {
+        if ($form->isSubmitted() && $form->isValid()) {
             // $form->getData() holds the submitted values
             // but, the original `$task` variable has also been updated
             $task = $form->getData();