Fix null pointer (issue 24790)

pkg/analyzer/lib/src/context/context.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.context.context;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'package:analyzer/instrumentation/instrumentation.dart';
@@ skipping 1030 matching lines @@
     if (sources != null) {
       for (Source source in sources) {
         getCacheEntry(source).setState(HINTS, CacheState.INVALID);
       }
     }
   }
 
   @override
   bool isClientLibrary(Source librarySource) {
     CacheEntry entry = _cache.get(librarySource);
-    return _referencesDartHtml(librarySource) && entry.getValue(IS_LAUNCHABLE);
+    return entry != null &&
+        _referencesDartHtml(librarySource) &&
+        entry.getValue(IS_LAUNCHABLE);
   }
 
   @override
   bool isServerLibrary(Source librarySource) {
     CacheEntry entry = _cache.get(librarySource);
-    return !_referencesDartHtml(librarySource) && entry.getValue(IS_LAUNCHABLE);
+    return entry != null &&
+        !_referencesDartHtml(librarySource) &&
+        entry.getValue(IS_LAUNCHABLE);
   }
 
   @override
   Stream<ComputedResult> onResultComputed(ResultDescriptor descriptor) {
     return driver.onResultComputed(descriptor);
   }
 
   @override
   CompilationUnit parseCompilationUnit(Source source) {
     if (!AnalysisEngine.isDartFileName(source.shortName)) {
@@ skipping 1067 matching lines @@
     DartSdk sdk = factory.dartSdk;
     if (sdk == null) {
       throw new IllegalArgumentException(
           "The source factory for an SDK analysis context must have a DartUriResolver");
     }
     return new AnalysisCache(<CachePartition>[
       AnalysisEngine.instance.partitionManager_new.forSdk(sdk)
     ]);
   }
 }