Revert "Void is not required to be `null` anymore."

pkg/compiler/lib/src/ssa/nodes.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.
 
 import '../closure.dart';
 import '../common.dart';
 import '../common_elements.dart' show CommonElements;
 import '../compiler.dart' show Compiler;
 import '../constants/constant_system.dart';
 import '../constants/values.dart';
@@ skipping 1324 matching lines @@
 
   HInstruction convertType(ClosedWorld closedWorld, DartType type, int kind) {
     if (type == null) return this;
     type = type.unaliased;
     // Only the builder knows how to create [HTypeConversion]
     // instructions with generics. It has the generic type context
     // available.
     assert(!type.isTypeVariable);
     assert(type.treatAsRaw || type.isFunctionType);
     if (type.isDynamic) return this;
-    if (type.isVoid) return this;
     if (type == closedWorld.commonElements.objectType) return this;
-    if (type.isFunctionType || type.isMalformed) {
+    if (type.isVoid || type.isFunctionType || type.isMalformed) {
       return new HTypeConversion(
           type, kind, closedWorld.commonMasks.dynamicType, this);
     }
     assert(type.isInterfaceType);
     if (kind == HTypeConversion.BOOLEAN_CONVERSION_CHECK) {
       // Boolean conversion checks work on non-nullable booleans.
       return new HTypeConversion(
           type, kind, closedWorld.commonMasks.boolType, this);
     } else if (kind == HTypeConversion.CHECKED_MODE_CHECK && !type.treatAsRaw) {
       throw 'creating compound check to $type (this = ${this})';
@@ skipping 2187 matching lines @@
   // ignore: MISSING_RETURN
   String get kindAsString {
     switch (kind) {
       case TypeInfoExpressionKind.COMPLETE:
         return 'COMPLETE';
       case TypeInfoExpressionKind.INSTANCE:
         return 'INSTANCE';
     }
   }
 }