title: Enzyme shallow renderer returns null node element
body: <p>I have a problem with Enzyme shallow renderer. My <code>wrapper.root.node</code> returning me null even for simple div element.</p>
  
  <pre><code>        const wrapper = shallow(
              &lt;div&gt;asd&lt;/div&gt;
          );
  </code></pre>
  
  <p>And here is ShallowWrapper object. Node element is null, but unrendered property contains normal rendered object. Why is that ? </p>
  
  <pre><code>ShallowWrapper {
    "complexSelector": ComplexSelector {
      "buildPredicate": [Function],
      "childrenOfNode": [Function],
      "findWhereUnwrapped": [Function],
    },
    "length": 1,
    "node": null,
    "nodes": Array [
      null,
    ],
    "options": Object {},
    "renderer": ReactShallowRenderer {
      "_instance": null,
      "getRenderOutput": [Function],
      "render": [Function],
    },
    "root": [Circular],
    "unrendered": &lt;div&gt;
      asd
  &lt;/div&gt;,
  }
  </code></pre>