code: public function getConverter()
      {
          if ($this->_converter === null) {
              $this->_converter = Yii::createObject(AssetConverter::className());
          } elseif (is_array($this->_converter) || is_string($this->_converter)) {
              if (is_array($this->_converter) && !isset($this->_converter['class'])) {
                  $this->_converter['class'] = AssetConverter::className();
              }
              $this->_converter = Yii::createObject($this->_converter);
          }
  
          return $this->_converter;
      }
docs: Returns the asset converter.
  @return AssetConverterInterface the asset converter.