Fix NPE when there is no keyword (issue 26630)

pkg/analysis_server/lib/src/services/correction/assist_internal.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 services.src.correction.assist;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'package:analysis_server/plugin/edit/assist/assist_core.dart';
@@ skipping 320 matching lines @@
       _coverageMarker();
       return;
     }
     // type source might be null, if the type is private
     if (typeSource == null) {
       _coverageMarker();
       return;
     }
     // add edit
     Token keyword = declarationList.keyword;
-    if (keyword.keyword == Keyword.VAR) {
+    if (keyword?.keyword == Keyword.VAR) {
       SourceRange range = rangeToken(keyword);
       _addReplaceEdit(range, typeSource);
     } else {
       _addInsertEdit(variable.offset, '$typeSource ');
     }
     // add proposal
     _addAssist(DartAssistKind.ADD_TYPE_ANNOTATION, []);
   }
 
   void _addProposal_assignToLocalVariable() {
@@ skipping 1787 matching lines @@
 class _SimpleIdentifierRecursiveAstVisitor extends RecursiveAstVisitor {
   final _SimpleIdentifierVisitor visitor;
 
   _SimpleIdentifierRecursiveAstVisitor(this.visitor);
 
   @override
   visitSimpleIdentifier(SimpleIdentifier node) {
     visitor(node);
   }
 }