Issue 24338. Don't propose creating a local class for prefixed identifiers.

pkg/analysis_server/lib/src/services/correction/fix_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 analysis_server.src.services.correction.fix_internal;
 
 import 'dart:collection';
 import 'dart:core' hide Resource;
 
 import 'package:analysis_server/edit/fix/fix_core.dart';
@@ skipping 434 matching lines @@
 
   void _addFix_createClass() {
     Element prefixElement = null;
     String name = null;
     SimpleIdentifier nameNode;
     if (node is SimpleIdentifier) {
       AstNode parent = node.parent;
       if (parent is PrefixedIdentifier) {
         PrefixedIdentifier prefixedIdentifier = parent;
         prefixElement = prefixedIdentifier.prefix.staticElement;
+        if (prefixElement == null) {
+          return;
+        }
         parent = prefixedIdentifier.parent;
         nameNode = prefixedIdentifier.identifier;
         name = prefixedIdentifier.identifier.name;
       } else {
         nameNode = node;
         name = nameNode.name;
       }
       if (!_mayBeTypeIdentifier(nameNode)) {
         return;
       }
@@ skipping 2282 matching lines @@
 /**
  * Describes the location for a newly created [FieldDeclaration].
  */
 class _FieldLocation {
   final String prefix;
   final int offset;
   final String suffix;
 
   _FieldLocation(this.prefix, this.offset, this.suffix);
 }