Void is not required to be `null` anymore.

pkg/compiler/lib/src/inferrer/type_graph_nodes.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library compiler.src.inferrer.type_graph_nodes;
 
 import 'dart:collection' show IterableBase;
 
 import '../common.dart';
 import '../common/names.dart' show Identifiers;
@@ skipping 1735 matching lines @@
   T visitClosureTypeInformation(ClosureTypeInformation info);
   T visitAwaitTypeInformation(AwaitTypeInformation info);
   T visitYieldTypeInformation(YieldTypeInformation info);
 }
 
 TypeMask _narrowType(
     ClosedWorld closedWorld, TypeMask type, ResolutionDartType annotation,
     {bool isNullable: true}) {
   if (annotation.treatAsDynamic) return type;
   if (annotation.isObject) return type;
+  if (annotation.isVoid) return type;
   TypeMask otherType;
   if (annotation.isTypedef || annotation.isFunctionType) {
     otherType = closedWorld.commonMasks.functionType;
   } else if (annotation.isTypeVariable) {
     // TODO(ngeoffray): Narrow to bound.
     return type;
-  } else if (annotation.isVoid) {
-    otherType = closedWorld.commonMasks.nullType;
   } else {
     ResolutionInterfaceType interfaceType = annotation;
     otherType = new TypeMask.nonNullSubtype(interfaceType.element, closedWorld);
   }
   if (isNullable) otherType = otherType.nullable();
   if (type == null) return otherType;
   return type.intersection(otherType, closedWorld);
 }