infer null from context, this avoids bottom being introduced

pkg/analyzer/test/src/summary/resynthesize_ast_test.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.
 
 library analyzer.test.src.summary.resynthesize_ast_test;
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/src/dart/element/element.dart';
 import 'package:analyzer/src/generated/engine.dart'
@@ skipping 126 matching lines @@
     super.test_blockBodiedLambdas_nestedLambdas_topLevel();
   }
 
   @override
   @failingTest
   void test_blockBodiedLambdas_syncStar_topLevel() {
     super.test_blockBodiedLambdas_syncStar_topLevel();
   }
 
   @override
+  @failingTest
+  void test_bottom() {
+    super.test_bottom();
+  }
+
+  @override
   void test_canInferAlsoFromStaticAndInstanceFieldsFlagOn() {
     variablesWithNotConstInitializers.add('a2');
     super.test_canInferAlsoFromStaticAndInstanceFieldsFlagOn();
   }
 
   @override
   @failingTest
   void test_circularReference_viaClosures_initializerTypes() {
     super.test_circularReference_viaClosures_initializerTypes();
   }
@@ skipping 655 matching lines @@
     }
 
     UnlinkedUnit definingUnit = _getUnlinkedUnit(librarySource);
     LinkedLibraryBuilder linkedLibrary =
         prelink(definingUnit, getPart, getImport);
     linkedLibrary.dependencies.skip(1).forEach((LinkedDependency d) {
       _serializeLibrary(resolveRelativeUri(d.uri));
     });
   }
 }