title: jstree wont save state if the data not defined in core?
body: <p>I have an application that is using jstree. In this app I have set the “data” section of core to an empty array as you see below: </p>
  
  <pre><code>$("#jstree")
      .jstree({
          "core": {
              "data": [],
              "check_callback" : true,
              "themes": {
                  "theme": "default",
                  "icons": false
              }
          },
          "plugins": [ "state" ]
      })
  </code></pre>
  
  <p>I am using jstree.create_node() to add new nodes to the tree programmatically as new data is sent to the browser. When I refresh the page the tree does not maintain the state even though I am using the state plugin. However if I set the <code>data</code> field in core to an actual JSON object, it would work as described in the <code>state</code> plugin:</p>
  
  <pre><code> "core": {
              "data":[{"id":"a", "parent":"#", "text":"nodeA"},{"id":"b", "parent":"a", "text":"nodeB"}],
              "check_callback" : true,
              "themes": {
                  "theme": "default",
                  "icons": false
              }
  </code></pre>
  
  <p>Is there a difference between the two ways of doing it that affects the state plugin? 
  Thanks!</p>