title: Invalid prop `selected` of type `String` supplied to `Calendar`, expected instance of `Date`?
body: <p>I am using date picker In react js
  <a href="https://www.npmjs.com/package/react-datepicker" rel="nofollow noreferrer">https://www.npmjs.com/package/react-datepicker</a>
  but my current value is blank <code>null</code> .Now I want to show date picker when I focus to <code>input field</code> .but I am getting error/warning this why ?</p>
  
  <pre><code>proxyConsole.js:72 Warning: Failed prop type: Invalid prop `selected` of type `String` supplied to `Calendar`, expected instance of `Date`.
      in Calendar (created by OnClickOutside(Calendar))
      in OnClickOutside(Calendar) (created by DatePicker)
      in div (created by InnerPopper)
      in InnerPopper (created by Context.Consumer)
      in Popper (created by PopperComponent)
      in Manager (created by PopperComponent)
      in PopperComponent (created by DatePicker)
      in DatePicker (created by Main)
  </code></pre>
  
  <p>Actually I added one condition while transforming the data</p>
  
  <pre><code> data[i].displaytext = i;
          if (data[i].dataType === "DATE" &amp;&amp; data[i].value) {
            data[i].value = new Date(data[i].value);
          }
          obj[lastLabel] = [...obj[lastLabel], data[i]];
        }
  </code></pre>
  
  <p>here is my code
  <a href="https://codesandbox.io/s/rmx02zzr5o" rel="nofollow noreferrer">https://codesandbox.io/s/rmx02zzr5o</a></p>
  
  <p>Please help me to remove this warning </p>