Fix kernel/visitor_test

pkg/compiler/lib/src/ssa/kernel_impact.dart

 // Copyright (c) 2016, 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 'package:kernel/ast.dart' as ir;
 
 import '../common.dart';
 import '../common/names.dart';
 import '../compiler.dart';
 import '../constants/expressions.dart';
@@ skipping 89 matching lines @@
       checkType(node.returnType);
     }
     node.positionalParameters.forEach(handleParameter);
     node.namedParameters.forEach(handleParameter);
   }
 
   ResolutionImpact buildField(ir.Field field) {
     checkType(field.type);
     if (field.initializer != null) {
       visitNode(field.initializer);
-      if (!field.isInstanceMember && !field.isConst) {
+      if (!field.isInstanceMember &&
+          !field.isConst &&
+          field.initializer is! ir.NullLiteral) {
         impactBuilder.registerFeature(Feature.LAZY_FIELD);
       }
-    } else {
-      impactBuilder.registerFeature(Feature.FIELD_WITHOUT_INITIALIZER);
     }
     if (field.isInstanceMember && astAdapter.isNative(field.enclosingClass)) {
       impactBuilder
           .registerNativeData(astAdapter.getNativeBehaviorForFieldLoad(field));
       impactBuilder
           .registerNativeData(astAdapter.getNativeBehaviorForFieldStore(field));
     }
     return impactBuilder;
   }
 
@@ skipping 443 matching lines @@
     Element target = astAdapter.getElement(node.target).declaration;
     impactBuilder.registerStaticUse(new StaticUse.superConstructorInvoke(
         target, astAdapter.getCallStructure(node.arguments)));
   }
 
   // TODO(johnniwinther): Make this throw and visit child nodes explicitly
   // instead to ensure that we don't visit unwanted parts of the ir.
   @override
   void defaultNode(ir.Node node) => node.visitChildren(this);
 }