[FEATURE] Make Node->depth actually initialized and usable

Actually initializes already present Node->depth property.

Fixes: #4216

Author: snk-spo

Classes/Domain/Search/ResultSet/Facets/OptionBased/Hierarchy/Node.php

@@ -22,7 +22,7 @@
  */
 class Node extends AbstractOptionFacetItem
 {
-    protected int $depth;
+    protected int $depth = 0;
 
     public function __construct(
         HierarchyFacet $facet,
@@ -41,6 +41,10 @@ public function __construct(
             $documentCount,
             $selected,
         );
+
+        if ($parentNode) {
+            $this->depth = $parentNode->getDepth() + 1;
+        }
     }
 
     public function getKey(): string
@@ -68,6 +72,11 @@ public function getHasParentNode(): bool
         return $this->parentNode !== null;
     }
 
+    public function getDepth(): int
+    {
+        return $this->depth;
+    }
+
     public function getHasChildNodeSelected(): bool
     {
         /** @var Node $childNode */