One more fix for SummaryTypeProvider - nullType is lazy.

pkg/analyzer/lib/src/summary/summary_sdk.dart

 // Copyright (c) 2015, 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 analyzer.src.summary.summary_sdk;
 
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
 import 'package:analyzer/src/context/cache.dart' show CacheEntry;
 import 'package:analyzer/src/context/context.dart';
@@ skipping 332 matching lines @@
   @override
   InterfaceType get futureDynamicType {
     assert(_asyncLibrary != null);
     _futureDynamicType ??= futureType.instantiate(<DartType>[dynamicType]);
     return _futureDynamicType;
   }
 
   @override
   InterfaceType get futureNullType {
     assert(_asyncLibrary != null);
-    _futureNullType ??= futureType.instantiate(<DartType>[_nullType]);
+    _futureNullType ??= futureType.instantiate(<DartType>[nullType]);
     return _futureNullType;
   }
 
   @override
   InterfaceType get futureType {
     assert(_asyncLibrary != null);
     _futureType ??= _getType(_asyncLibrary, "Future");
     return _futureType;
   }
 
@@ skipping 139 matching lines @@
    * throw a [StateError] if there is no class with the given name.
    */
   InterfaceType _getType(LibraryElement library, String name) {
     Element element = library.getType(name);
     if (element == null) {
       throw new StateError("No definition of type $name");
     }
     return (element as ClassElement).type;
   }
 }