title: Treegrid mode not working with free-jqgrid 4.9.0
body: <p>I have the following treegrid working perfectly with jqGrid v4.5.2:</p>
  
  <pre><code>${"#tree").jqGrid({
    url: "/tree",
    datatype : "json",
    colModel : [{
      name: "data.id",
      key: true
    }, {
      name: "data.name"
    }],
    colNames : [],
    jsonReader : {
      page : 1,
      records : "total",
      repeatitems : false,
      root : "nodes",
      total : 1
    },
    treeGrid : true,
    treeGridModel : "adjacency",
    tree_root_level : 1,
    ExpandColumn : "data.id",
    ExpandColClick : true,
    treeReader : {
      leaf_field : "leaf",
      parent_id_field : "data.parentId"
  });
  </code></pre>
  
  <p>The first data payload from the server is:</p>
  
  <pre><code>{
    "pageIndex": 1,
    "pageSize": 100
    "pages": 290,
    "total": 2891,
    "nodes": [
      {
        "data": { "id": 1, "name": "Node 1", "leaf": false },
        "errors": []
      },
      {
        "data": { "id": 2, "name": "Node 2", "leaf": false },
        "errors": []
      }
    ]
  }
  </code></pre>
  
  <p>However, this same code does not work with free-jqgrid v4.9.0. Nothing happens when a node is expanded - no JavaScript error is seen in the browser console, no request is sent to the server, no other action takes place.</p>