Handle null literal in compile_from_dill

pkg/compiler/lib/src/universe/world_builder.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 world_builder;
 
 import 'dart:collection';
 
 import '../common.dart';
 import '../common/names.dart' show Identifiers;
 import '../common/resolution.dart' show Resolution;
 import '../common_elements.dart';
+import '../constants/constant_system.dart';
 import '../constants/values.dart';
 import '../elements/elements.dart';
 import '../elements/entities.dart';
 import '../elements/resolution_types.dart';
 import '../elements/types.dart';
 import '../js_backend/backend.dart' show JavaScriptBackend;
 import '../js_backend/backend_usage.dart' show BackendUsageBuilder;
 import '../js_backend/constant_handler_javascript.dart'
     show JavaScriptConstantCompiler;
 import '../js_backend/interceptor_data.dart' show InterceptorDataBuilder;
@@ skipping 155 matching lines @@
 
   /// All directly instantiated types, that is, the types of the directly
   /// instantiated classes.
   // TODO(johnniwinther): Improve semantic precision.
   Iterable<InterfaceType> get instantiatedTypes;
 
   /// Registers that [type] is checked in this world builder. The unaliased type
   /// is returned.
   void registerIsCheck(DartType type);
 }