public function __construct($children = null)
 {
     if ($children instanceof FieldList) {
         $this->children = $children;
     } elseif (is_array($children)) {
         $this->children = new FieldList($children);
     } else {
         //filter out null/empty items
         $children = array_filter(func_get_args());
         $this->children = new FieldList($children);
     }
     $this->children->setContainerField($this);
     parent::__construct(null, false);
 }