[BUGFIX] Do not render empty link explanation callout

In case a link does not set any additional
attributes, no empty callout is rendered.

Resolves: #102721
Releases: main, 12.4
Change-Id: I7ec4d7b64450112731363d721f4d49322448b41c
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/82280


Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Benni Mack <benni@typo3.org>

typo3/sysext/backend/Classes/Form/Element/LinkElement.php

@@ -431,13 +431,15 @@ class LinkElement extends AbstractFormElement
                 ];
         }
 
-        $data['additionalAttributes'] = '
-            <div class="callout callout-info mt-3 mb-0">
-                <div class="callout-body">
-                    ' . implode(' - ', $additionalAttributes) . '
+        $data['additionalAttributes'] = $additionalAttributes !== []
+            ? '
+                <div class="callout callout-info mt-3 mb-0">
+                    <div class="callout-body">
+                        ' . implode(' - ', $additionalAttributes) . '
+                    </div>
                 </div>
-            </div>
-        ';
+            '
+            : ''; // Ensure "additionalAttributes" is always set (bw compatibility for the event)
 
         return $this->eventDispatcher->dispatch(
             new ModifyLinkExplanationEvent($data, $linkData, $linkParts, $this->data)