Void is not required to be `null` anymore.

pkg/compiler/lib/src/js_backend/backend.dart

 // Copyright (c) 2012, 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 js_backend.backend;
 
 import 'dart:async' show Future;
 
 import 'package:js_runtime/shared/embedded_names.dart' as embeddedNames;
 
@@ skipping 2060 matching lines @@
           transformed, impacts.functionTypeCheck);
     }
     if (type.element != null && backend.isNative(type.element)) {
       backendUsage.registerBackendImpact(transformed, impacts.nativeTypeCheck);
     }
   }
 
   void onIsCheckForCodegen(
       ResolutionDartType type, TransformedWorldImpact transformed) {
     if (type.isDynamic) return;
+    if (type.isVoid) return;
     type = type.unaliased;
     backendUsage.registerBackendImpact(transformed, impacts.typeCheck);
 
     bool inCheckedMode = backend.compiler.options.enableTypeAssertions;
     // [registerIsCheck] is also called for checked mode checks, so we
     // need to register checked mode helpers.
     if (inCheckedMode) {
       // All helpers are added to resolution queue in enqueueHelpers. These
       // calls to [enqueue] with the resolution enqueuer serve as assertions
       // that the helper was in fact added.
@@ skipping 630 matching lines @@
   WorldImpact registerInstantiatedClass(ClassEntity cls) {
     WorldImpact worldImpact = _processClass(cls, forResolution: false);
     lookupMapAnalysis.registerInstantiatedClass(cls);
     return worldImpact;
   }
 
   // TODO(johnniwinther): Avoid the need for accessing [_backend].
   bool methodNeedsRti(FunctionElement function) =>
       _backend.methodNeedsRti(function);
 }