B2B-2469: Improve category children loading

- functional fixes

Author: rganin

app/code/Magento/CatalogGraphQl/Model/Resolver/Products/DataProvider/CategoryTree/Wrapper/Node.php

@@ -100,19 +100,25 @@ public function getId(): int
 
     /**
      * Render node and its children as an array recursively.
+     * Returns null is node model is not set.
      *
-     * @return array
+     * @return array|null
      */
-    public function renderArray(): array
+    public function renderArray(): ?array
     {
+        if (!$this->model) {
+            return null;
+        }
         return array_merge(
             $this->forgery->getHydrator()->hydrateCategory($this->model),
             [
-                'children' => array_map(
-                    function ($node) {
-                        return $node->renderArray();
-                    },
-                    $this->children
+                'children' => array_filter(
+                    array_map(
+                        function ($node) {
+                            return $node->renderArray();
+                        },
+                        $this->children
+                    )
                 )
             ]
         );

app/code/Magento/CatalogGraphQl/Model/Resolver/Products/DataProvider/ExtractDataFromCategoryTree.php

@@ -10,9 +10,26 @@
 use Magento\Catalog\Model\Category;
 use Magento\Catalog\Model\ResourceModel\Category\Collection;
 use Magento\CatalogGraphQl\Model\Resolver\Products\DataProvider\CategoryTree\Wrapper\Forgery;
+use Magento\CatalogGraphQl\Model\Resolver\Products\DataProvider\CategoryTree\Wrapper\ForgeryFactory;
 
+/**
+ * Data extractor for category tree processing in GraphQL resolvers.
+ */
 class ExtractDataFromCategoryTree
 {
+    /**
+     * @var ForgeryFactory
+     */
+    private $resultTreeForgeryFactory;
+
+    /**
+     * @param ForgeryFactory $resultTreeForgeryFactory
+     */
+    public function __construct(ForgeryFactory $resultTreeForgeryFactory)
+    {
+        $this->resultTreeForgeryFactory = $resultTreeForgeryFactory;
+    }
+
     /**
      * Build result tree from collection
      *
@@ -22,7 +39,8 @@ class ExtractDataFromCategoryTree
      */
     public function buildTree(Collection $collection, array $topLevelCategories) : array
     {
-        $forgery = new Forgery();
+        /** @var Forgery $forgery */
+        $forgery = $this->resultTreeForgeryFactory->create();
         /** @var Category $item */
         foreach ($collection->getItems() as $item) {
             $forgery->forge($item);