Remove special list behavior in analysis server protocol.

pkg/analysis_server/test/integration/analysis/overrides_test.dart

 // Copyright (c) 2014, 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 test.integration.analysis.overrides;
 
 import 'package:analysis_server/src/protocol.dart';
 import 'package:unittest/unittest.dart';
 
 import '../../reflective_tests.dart';
@@ skipping 83 matching lines @@
           Set<String> actualOverridesInterfaces = new Set<String>();
           for (OverriddenMember overriddenMember in interfaceMembers) {
             expect(overriddenMember.element.name, equals(methodName));
             String className = overriddenMember.className;
             bool wasAdded = actualOverridesInterfaces.add(className);
             expect(wasAdded, isTrue);
           }
           expect(actualOverridesInterfaces, equals(
               expectedOverridesInterfaces.toSet()));
         } else {
-          // TODO(paulberry): As a result of bug 21230, an Override with a
-          // missing interfaceMembers field is misinterpreted as having an
-          // interfaceMembers field which is an empty list.  Once bug 21230 is
-          // fixed this should be an "isNull" check.
-          expect(interfaceMembers, isEmpty);
+          expect(interfaceMembers, isNull);
         }
       }
       checkOverrides('method0', true, ['Interface1', 'Interface2']);
       checkOverrides('method1', false, ['Interface1', 'Interface2']);
       checkOverrides('method2', true, ['Interface1']);
       checkOverrides('method3', false, ['Interface1']);
       checkOverrides('method4', true, ['Interface2']);
       checkOverrides('method5', false, ['Interface2']);
       checkOverrides('method6', true, []);
       checkOverrides('method7', false, []);
     });
   }
 }
 
 main() {
   runReflectiveTests(Test);
 }