5b: Throw an Exception is a non-article is wrapped

Within the article wrapper, let’s check that the node is an article,
otherwise thrown the Exception as expected.

web/modules/custom/my_module/src/Wrapper/ArticleWrapper.php

@@ -9,6 +9,8 @@ class ArticleWrapper {
   private $article;
 
   public function __construct(NodeInterface $node) {
+    $this->verifyNodeType($node);
+
     $this->article = $node;
   }
 
@@ -16,4 +18,13 @@ class ArticleWrapper {
     return $this->article;
   }
 
+  private function verifyNodeType(NodeInterface $node): void {
+   if ($node->bundle() != 'article') {
+     throw new \InvalidArgumentException(sprintf(
+         '%s is not an article',
+         $node->bundle()
+       ));
+    }
+  }
+
 }