title: summernote prints "node is null" when initialized
body: <p>I am building a form with summernote <code>v0.7.3</code>.</p>
  
  <p>Works fine in chrome, but in firefox it give an err "node is null".</p>
  
  <pre><code>&lt;div id="${id}_summernote"&gt;&lt;/div&gt;
  &lt;script type="text/javascript"&gt;
    $(document).ready(function(){ 
      var s_note = $('#${id}_summernote');
      var summernote = s_note.summernote();
    }
  &lt;/script&gt;
  </code></pre>
  
  <p>The point where the error occurs is ..</p>
  
  <pre><code>var nodeLength = function (node) {
    if (isText(node)) {
      return node.nodeValue.length;
    }
  
    return node.childNodes.length;
  };
  </code></pre>
  
  <p>it is line 614 in <code>summernote.js</code>. </p>
  
  <p>After that since <code>node is null</code>, other error messages are also showed up</p>
  
  <pre><code>ImagePopover/this.hide()
   summernote.js:6152
  ImagePopover/this.update()
   summernote.js:6147
  Context/this.invoke()
   summernote.js:1687
  Handle/this.update()
   summernote.js:4903
  Handle/this.events["summernote.mousedown"]()
   summernote.js:4841
  n.event.dispatch()
   jquery-2.1.1.min.js:3
  n.event.add/r.handle()
   jquery-2.1.1.min.js:3
  n.event.trigger()
   jquery-2.1.1.min.js:3
  .trigger/&lt;()
   jquery-2.1.1.min.js:3
  .each()
   jquery-2.1.1.min.js:2
  n.prototype.each()
   jquery-2.1.1.min.js:2
  .trigger()
   jquery-2.1.1.min.js:3
  Context/this.triggerEvent()
   summernote.js:1604
  Editor/this.initialize/&lt;()
   summernote.js:3745
  n.event.dispatch()
   jquery-2.1.1.min.js:3
  n.event.add/r.handle()
   jquery-2.1.1.min.js:3
  </code></pre>
  
  <p>What should I do to fix this? It happens to some of the pages, not all.</p>
  
  <p>Thanks for the answer!</p>