Fix an exception caused by malformed code

pkg/analyzer/test/src/context/context_test.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 analyzer.test.src.context.context_test;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 472 matching lines @@
 ''');
     LibraryElement libraryElement = context.computeLibraryElement(source);
     expect(libraryElement, isNotNull);
     expect(context.computeDocumentationComment(libraryElement), comment);
   }
 
   void test_computeDocumentationComment_null() {
     expect(context.computeDocumentationComment(null), isNull);
   }
 
+  void test_computeErrors_dart_malformedCode() {
+    Source source = addSource("/lib.dart", "final int , = 42;");
+    List<AnalysisError> errors = context.computeErrors(source);
+    expect(errors, isNotNull);
+    expect(errors.length > 0, isTrue);
+  }
+
   void test_computeErrors_dart_none() {
     Source source = addSource("/lib.dart", "library lib;");
     List<AnalysisError> errors = context.computeErrors(source);
     expect(errors, hasLength(0));
   }
 
   void test_computeErrors_dart_part() {
     Source librarySource =
         addSource("/lib.dart", "library lib; part 'part.dart';");
     Source partSource = addSource("/part.dart", "part of 'lib';");
@@ skipping 2368 matching lines @@
    * Initialize the visitor.
    */
   _ElementGatherer();
 
   @override
   void visitElement(Element element) {
     elements[element] = element;
     super.visitElement(element);
   }
 }