title: react ref value is empty
body: <p>I have a react component with an uncontrolled input element like below:</p>
  
  <pre><code>class TestComponent {
  
  onAddTypeClicked = el =&gt; {
      console.log(el);
      console.log(el.value);
  };
  
  
  render() {
      return (
          &lt;div&gt;
              &lt;input
                  name="asset_types"
                  ref={el =&gt; this.assetTypesAdd = el}
              /&gt;
              &lt;button
                  type="button"
                  onClick={e =&gt; this.onAddTypeClicked(this.assetTypesAdd)}
              /&gt;   
          &lt;/div&gt;
      );
  }
  </code></pre>
  
  <p>Now when I type some value in input field and click button, the input is getting printed correctly but it's value is empty. It works fine if I use document.getElementById approach though. Can anyone point if I'm doing anything wrong, please?</p>