public function obj()
    {
        if ($this->obj === null) {
            $formGroup = $this->formGroup();
            if ($formGroup instanceof self) {
                $prop = $formGroup->storageProperty();
                $val  = $formGroup->obj()->propertyValue($prop->ident());

                $this->obj = $prop->structureVal($val, [ 'default_data' => true ]);
                if ($this->obj === null) {
                    $this->obj = clone $prop->structureProto();
                }
            } elseif ($this->form() instanceof ObjectContainerInterface) {
                $this->obj = $this->form()->obj();
            }

            if ($this->obj === null) {
                throw new RuntimeException(sprintf(
                    'The [%1$s] widget has no data model.',
                    static::CLASS
                ));
            }
        }

        return $this->obj;
    }