#220 The getChildren() function now always returns an array, and it u…

…ses the children() function of the Doctrine Tree extension to return the direct children of a Collection instance

library/Opus/Model2/Collection.php

@@ -210,11 +210,17 @@ public function setParent($parent)
     }
 
     /**
-     * @return ORMCollection|self[]
+     * Returns all child nodes. Always returns an array, even if the result set has zero or one element.
+     *
+     * @return self[]
      */
     public function getChildren()
     {
-        return $this->children;
+        // TODO DOCTRINE The $this->children property is currently unused
+
+        $children = self::getRepository()->children($this, true, 'left');
+
+        return $children ?: [];
     }
 
     /**