Guard against getting a watch event before the driver is created (issue 30333)

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/plugin/notification_manager.dart';
@@ skipping 901 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);
-      SourceFactory factory = builder.createSourceFactory(contextRoot, options);
       AnalysisDriver driver = info.analysisDriver;
-      driver.configure(analysisOptions: options, sourceFactory: factory);
+      if (driver != null) {
+        AnalysisOptions options = builder.getAnalysisOptions(contextRoot,
+            contextRoot: driver.contextRoot);
+        SourceFactory factory =
+            builder.createSourceFactory(contextRoot, options);
+        driver.configure(analysisOptions: options, sourceFactory: factory);
+      }
     }
   }
 
   /**
    * Compute the set of files that are being flushed, this is defined as
    * the set of sources in the removed context (context.sources), that are
    * orphaned by this context being removed (no other context includes this
    * file.)
    */
   List<String> _computeFlushedFiles(ContextInfo info) {
@@ skipping 852 matching lines @@
     }
     return _embedderLocator;
   }
 
   @override
   SdkExtensionFinder getSdkExtensionFinder(ResourceProvider resourceProvider) {
     return _sdkExtensionFinder ??=
         new SdkExtensionFinder(buildPackageMap(resourceProvider));
   }
 }