Fix for NPE if subscribing for errors in a not analyzed file.

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:analyzer/file_system/file_system.dart';
@@ skipping 452 matching lines @@
   /**
    * Implementation for `analysis.setSubscriptions`.
    */
   void setAnalysisSubscriptions(Map<AnalysisService, Set<String>> subscriptions) {
     // send notifications for already analyzed sources
     subscriptions.forEach((service, Set<String> newFiles) {
       Set<String> oldFiles = analysisServices[service];
       Set<String> todoFiles = oldFiles != null ? newFiles.difference(oldFiles) : newFiles;
       for (String file in todoFiles) {
         Source source = getSource(file);
+        // prepare context
         AnalysisContext context = getAnalysisContext(file);
+        if (context == null) {
+          continue;
+        }
         // errors
         if (service == AnalysisService.ERRORS) {
           LineInfo lineInfo = context.getLineInfo(source);
-          List<AnalysisError> errors = context.getErrors(source).errors;
-          sendAnalysisNotificationErrors(this, file, lineInfo, errors);
+          if (lineInfo != null) {
+            List<AnalysisError> errors = context.getErrors(source).errors;
+            sendAnalysisNotificationErrors(this, file, lineInfo, errors);
+          }
         }
         // Dart unit notifications.
         if (AnalysisEngine.isDartFileName(file)) {
           CompilationUnit dartUnit = getResolvedCompilationUnitToResendNotification(file);
           if (dartUnit != null) {
             switch (service) {
               case AnalysisService.HIGHLIGHTS:
                 sendAnalysisNotificationHighlights(this, file, dartUnit);
                 break;
               case AnalysisService.NAVIGATION:
@@ 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);
 }