Adding a new content element can fail with "Undefined array key 'allowedContentTypes'" in `ManipulateBackendLayoutColPosConfigurationForPage`

[einpraegsam]

When creating a new content element via the page module, the b13/container listener ManipulateBackendLayoutColPosConfigurationForPage can throw a PHP warning that escalates to an exception in the TYPO3 backend, blocking the form from opening:

TYPO3\CMS\Core\Error\Exception (1476107295)
PHP Warning: Undefined array key "allowedContentTypes" in vendor/b13/container/Classes/Listener/ManipulateBackendLayoutColPosConfigurationForPage.php line 46

The issue is conditional on an unlucky uid collision and reproduces reliably for us on TYPO3 14.3 / b13/container 4.0.0 / PHP 8.5.

Steps to reproduce

1. Have a container content element with at least one child (so tt_content row uid=N has tx_container_parent > 0 and colPos matching the registered grid column, e.g. 51).
2. On the same TYPO3 instance, navigate the page module to a page whose page uid equals N (i.e. same numeric value as the child's uid in step 1).
3. Click Create new content element in any non-container column on that page (e.g. colPos=0).
4. The backend redirects to the edit form URL with edit[tt_content][N]=new and the exception is rendered instead of the form.

A quick patch that does the trick for us:

fix-listener-new-command-and-missing-keys.patch

[alexanderschnitzler]

--- a/Classes/Listener/ManipulateBackendLayoutColPosConfigurationForPage.php
+++ b/Classes/Listener/ManipulateBackendLayoutColPosConfigurationForPage.php
@@ -43,8 +43,8 @@ class ManipulateBackendLayoutColPosConfigurationForPage
         $cType = $container->getCType();
         $configuration = $this->tcaRegistry->getContentDefenderConfiguration($cType, $e->colPos);
         $e->configuration = [
-            'allowedContentTypes' => $configuration['allowedContentTypes'],
-            'disallowedContentTypes' => $configuration['disallowedContentTypes'],
+            'allowedContentTypes' => $configuration['allowedContentTypes'] ?? '',
+            'disallowedContentTypes' => $configuration['disallowedContentTypes'] ?? '',
         ];
     }

I ran into this part of the bug as well when a container config was generated for a non registered colPos grid. So whatever that other part of the bug is, this fix here is a must have.