#3512736 Fix for null check.

Closes #3512736

modules/ai_chatbot/src/Plugin/Block/ChatFormBlock.php

@@ -12,6 +12,7 @@ use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
 use Drupal\Core\Access\AccessResult;
 use Drupal\Core\Session\AccountInterface;
 use Drupal\ai_chatbot\Form\ChatForm;
+use Drupal\ai_assistant_api\Entity\AiAssistant as AiAssistant;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 
 /**
@@ -262,8 +263,27 @@ class ChatFormBlock extends BlockBase implements ContainerFactoryPluginInterface
    * {@inheritdoc}
    */
   public function build() {
-    /** @var \Drupal\ai_assistant_api\Entity\AiAssistant */
-    $assistant = $this->entityTypeManager->getStorage('ai_assistant')->load($this->configuration['ai_assistant']);
+    // Load the AI Assistant entity.
+    $assistant_id = $this->configuration['ai_assistant'] ?? NULL;
+
+    // If no assistant ID is provided or it's invalid, handle it gracefully.
+    if (!is_string($assistant_id) || $assistant_id === "") {
+      return [
+        '#markup' => $this->t('No valid AI Assistant configured for this block.'),
+      ];
+    }
+
+    /** @var \Drupal\ai_assistant_api\Entity\AiAssistant|null */
+    $assistant = $this->entityTypeManager->getStorage('ai_assistant')->load($assistant_id);
+
+    // If the assistant still couldn't be loaded, handle the failure.
+    if (!$assistant instanceof AiAssistant) {
+      return [
+        '#markup' => $this->t('The specified AI Assistant could not be loaded.'),
+      ];
+    }
+
+    // Proceed with setting the assistant and building the block.
     $this->aiAssistantRunner->setAssistant($assistant);
     $this->aiAssistantRunner->streamedOutput($this->configuration['stream']);
     $block = [];