Completion breaks if core is not analyzed (issue 22814)

pkg/analysis_server/lib/src/services/completion/dart_completion_cache.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.completion.dart.cache;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'package:analysis_server/src/protocol_server.dart'
@@ skipping 180 matching lines @@
       }
     }
   }
 
   /**
    * Add suggestions for implicitly imported elements in dart:core.
    */
   void _addDartCoreSuggestions() {
     Source coreUri = context.sourceFactory.forUri('dart:core');
     LibraryElement coreLib = context.getLibraryElement(coreUri);
+    if (coreLib == null) {
+      // If the core library has not been analyzed yet, then we cannot add any
+      // suggestions from it.
+      return;
+    }
     Namespace coreNamespace =
         new NamespaceBuilder().createPublicNamespaceForLibrary(coreLib);
     coreNamespace.definedNames.forEach((String name, Element elem) {
       if (elem is ClassElement) {
         importedClassMap[name] = elem;
       }
       _addSuggestion(elem, DART_RELEVANCE_DEFAULT);
     });
   }
 
@@ skipping 167 matching lines @@
   @override
   void visitFunctionTypeAliasElement(FunctionTypeAliasElement element) {
     cache._addSuggestion(element, DART_RELEVANCE_DEFAULT);
   }
 
   @override
   void visitTopLevelVariableElement(TopLevelVariableElement element) {
     cache._addSuggestion(element, DART_RELEVANCE_DEFAULT);
   }
 }