title: why pixi.js set field to null when destroy?
body: <p>I have study pixi.js these day,and I noticed the destoy function was appear several in the source code,It looks like this.</p>
  
  <pre><code>/**
   * Removes everything from the renderer and optionally removes the Canvas DOM element.
   *
   * @param {boolean} [removeView=false] - Removes the Canvas element from the DOM.
   */
  destroy(removeView)
  {
      this.destroyPlugins();
  
      // call the base destroy
      super.destroy(removeView);
  
      this.context = null;
  
      this.refresh = true;
  
      this.maskManager.destroy();
      this.maskManager = null;
  
      this.smoothProperty = null;
  }
  </code></pre>
  
  <p>Why it need set field to null?In my opinion when the host Object be garbage collected,all the field will be auto garbage collected,so manually set field to null looks like useless.</p>
  
  <p>Because it was a famous framework,I think it may has some reason,can anyone tell me?</p>