Fix an npe in context_manager.dart.

pkg/analysis_server/lib/src/context_manager.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.
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:convert';
 import 'dart:core';
 
 import 'package:analysis_server/src/analysis_server.dart';
@@ skipping 1026 matching lines @@
 
   void _checkForPackagespecUpdate(
       String path, ContextInfo info, Folder folder) {
     // Check to see if this is the .packages file for this context and if so,
     // update the context's source factory.
     if (absolutePathContext.basename(path) == PACKAGE_SPEC_NAME) {
       String contextRoot = info.folder.path;
       ContextBuilder builder =
           callbacks.createContextBuilder(info.folder, defaultContextOptions);
       AnalysisOptions options = builder.getAnalysisOptions(contextRoot,
-          contextRoot: info.analysisDriver.contextRoot);
+          contextRoot: info?.analysisDriver?.contextRoot);

[Brian Wilkerson, 2017/05/30 21:39:47]

It would be good to understand why the info is null, because I wouldn't have
expected it to be null at this point. (For example, a quick look indicates that
we might have a path that isn't being analyzed, in which case we probably should
catch it earlier.)

       SourceFactory factory = builder.createSourceFactory(contextRoot, options);
       if (enableNewAnalysisDriver) {
         AnalysisDriver driver = info.analysisDriver;
         driver.configure(analysisOptions: options, sourceFactory: factory);
       } else {
         info.context.analysisOptions = options;
         info.context.sourceFactory = factory;
       }
     }
   }
@@ skipping 916 matching lines @@
     }
     return _embedderLocator;
   }
 
   @override
   SdkExtensionFinder getSdkExtensionFinder(ResourceProvider resourceProvider) {
     return _sdkExtensionFinder ??=
         new SdkExtensionFinder(buildPackageMap(resourceProvider));
   }
 }