title: ModelCache.computeIfAbsent must not be null
body: <p>After upgrading to Android Studio 3 Canary 4 I've got this error:</p>
  
  <blockquote>
    <p>Gradle sync failed: Argument for @NotNull parameter 'key' of
    com/android/tools/idea/gradle/project/model/ide/android/ModelCache.computeIfAbsent
    must not be null</p>
  </blockquote>
  
  <p>Anyone else has the same problem?</p>