Issue 24639. Check the correct object for null.

pkg/analyzer/lib/src/task/html_work_manager.dart

 // Copyright (c) 2015, 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.src.task.html_work_manager;
 
 import 'dart:collection';
 
 import 'package:analyzer/src/context/cache.dart';
 import 'package:analyzer/src/generated/engine.dart'
@@ skipping 213 matching lines @@
         htmlSources.add(target);
       }
       if (target is DartScript) {
         scriptTargets.add(target);
       }
     }
     // Invalidate targets and values.
     scriptTargets.forEach(partition.remove);
     for (Source htmlSource in htmlSources) {
       CacheEntry entry = partition.get(htmlSource);
-      if (htmlSource != null) {
+      if (entry != null) {
         entry.setState(HTML_ERRORS, CacheState.INVALID);
         if (invalidateUris) {
           entry.setState(REFERENCED_LIBRARIES, CacheState.INVALID);
         }
       }
     }
   }
 
   /**
    * Returns `true` if the given [result] of the given [target] needs
    * computing, i.e. it is not in the valid and not in the error state.
    */
   bool _needsComputing(AnalysisTarget target, ResultDescriptor result) {
     CacheState state = analysisCache.getState(target, result);
     return state != CacheState.VALID && state != CacheState.ERROR;
   }
 
   /**
    * Return `true` if the given target is an HTML source.
    */
   static bool _isHtmlSource(AnalysisTarget target) {
     return target is Source && AnalysisEngine.isHtmlFileName(target.fullName);
   }
 }