title: Kotlin null-check bug
body: <p>I use Java library. In exception class there is "localizedMessage" field and "description" field. I don't know why, but "description" (which is java String) is recognized as String! by Kotlin, and when "description" is null, condition description == null returns false.
  Example of code: </p>
  
  <pre><code>mvpView?.showToast(it.description?:it.localizedMessage)
  </code></pre>
  
  <p>or without Elvis:</p>
  
  <pre><code>if (it.description.isNullOrBlank()) {
       mvpView?.showToast(it.localizedMessage)
  } else {
       mvpView?.showToast(it.description)
  }
  </code></pre>
  
  <p>it always tries to show "description", but "evaluate expression" in debug mode returns true on description == null (as expected).</p>
  
  <p>Kotlin version is 1.1.1</p>