Handle null content in ContentChange.

pkg/analysis_server/lib/src/analysis_server.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 analysis.server;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'package:analysis_server/src/analysis_logger.dart';
@@ skipping 285 matching lines @@
                       requestId, e.message));
     }
   }
 
   /**
    * Implementation for `analysis.updateContent`.
    */
   void updateContent(Map<String, ContentChange> changes) {
     changes.forEach((file, change) {
       AnalysisContext analysisContext = _getAnalysisContext(file);
+      // TODO(paulberry): handle the case where a file is referred to by more
+      // than one context (e.g package A depends on package B using a local
+      // path, user has both packages open for editing in separate contexts,
+      // and user modifies a file in package B).
       if (analysisContext != null) {
         Source source = _getSource(file);
         if (change.offset == null) {
           analysisContext.setContents(source, change.content);
         } else {
           analysisContext.setChangedContents(source, change.content,
               change.offset, change.oldLength, change.newLength);
         }
         schedulePerformAnalysisOperation(analysisContext);
       }
@@ skipping 169 matching lines @@
 /**
  * An enumeration of the services provided by the server domain.
  */
 class ServerService extends Enum2<ServerService> {
   static const ServerService STATUS = const ServerService('STATUS', 0);
 
   static const List<ServerService> VALUES = const [STATUS];
 
   const ServerService(String name, int ordinal) : super(name, ordinal);
 }