minor #12242 [Form] no need to add the url listener when it does not …

…do anything (Tobion)

This PR was merged into the 2.3 branch.

Discussion
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[Form] no need to add the url listener when it does not do anything

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

In line with #11696

Commits
-------

7aea1c9 [Form] no need to add the url listener when it does not do anything

src/Symfony/Component/Form/Extension/Core/EventListener/FixUrlProtocolListener.php

@@ -24,6 +24,11 @@ class FixUrlProtocolListener implements EventSubscriberInterface
 {
     private $defaultProtocol;
 
+    /**
+     * Constructor.
+     *
+     * @param string|null $defaultProtocol The URL scheme to add when there is none or null to not modify the data
+     */
     public function __construct($defaultProtocol = 'http')
     {
         $this->defaultProtocol = $defaultProtocol;

src/Symfony/Component/Form/Extension/Core/Type/UrlType.php

@@ -23,7 +23,9 @@ class UrlType extends AbstractType
      */
     public function buildForm(FormBuilderInterface $builder, array $options)
     {
-        $builder->addEventSubscriber(new FixUrlProtocolListener($options['default_protocol']));
+        if (null !== $options['default_protocol']) {
+            $builder->addEventSubscriber(new FixUrlProtocolListener($options['default_protocol']));
+        }
     }
 
     /**