text: function NullRenderer( options ){
    this.options = options;
    this.notifications = 0; // for testing
  }
  
  let noop = function(){};
  
  let throwImgErr = function(){
    throw new Error('A headless instance can not render images');
  };
  
  NullRenderer.prototype = {
    recalculateRenderedStyle: noop,
    notify: function(){ this.notifications++; },
    init: noop,
    isHeadless: function(){ return true; },
    png: throwImgErr,
    jpg: throwImgErr
  };
  
  export default NullRenderer;
  