title: Warning "Must be one of" - NotificationManager.IMPORTANCE
body: <p>In Android Studio I get an error on <code>new NotificationChannel()</code>:  </p>
  
  <blockquote>
    <p>Must be one of: android.app.NotificationManager.IMPORTANCE_HIGH, android app.NotificationManager.IMPORTANCE_LOW, ...</p>
  </blockquote>
  
  <p>But I reference exactly this.<br>
  So it seems this is a bug in Android Studio.<br>
  Does anyone have the same problem?</p>
  
  <p><strong>Example:</strong>
  <a href="https://i.stack.imgur.com/TdO74.png" rel="noreferrer"><img src="https://i.stack.imgur.com/TdO74.png" alt="enter image description here"></a> </p>
  
  <p>And I know I can add an <code>@Suppress</code> annotation, but I want to clarify if it is an error or not.</p>
  
  <p><strong>CompileSDKVersion:</strong> 26<br>
  <strong>TargetSDKVersion:</strong> 26<br>
  <strong>Android Studio Version:</strong> 3.0.1</p>
  
  <p><strong>My Import:</strong><br>
  <a href="https://i.stack.imgur.com/ho56Q.png" rel="noreferrer"><img src="https://i.stack.imgur.com/ho56Q.png" alt="enter image description here"></a></p>