public function addData($data)
    {
        if (empty($this->_data)) {
            $this->_data = $data;
        } else {
            if (!is_array($this->_data)) {
                throw new \yii\base\Exception('Unable to merge existing data with new data. Existing data is not an array.');
            }
            $this->_data = array_merge($this->_data, $data);
        }
        return $this;
    }