Add 'Add != null' quick fix.

pkg/analysis_server/lib/src/services/correction/fix.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;
 
 import 'package:analysis_server/edit/fix/fix_core.dart';
 import 'package:analysis_server/src/plugin/server_plugin.dart';
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/src/generated/engine.dart';
@@ skipping 91 matching lines @@
   static const ADD_ASYNC =
       const FixKind('ADD_ASYNC', 50, "Add 'async' modifier");
   static const ADD_FIELD_FORMAL_PARAMETERS = const FixKind(
       'ADD_FIELD_FORMAL_PARAMETERS', 30, "Add final field formal parameters");
   static const ADD_MISSING_PARAMETER_POSITIONAL = const FixKind(
       'ADD_MISSING_PARAMETER_POSITIONAL',
       31,
       "Add optional positional parameter");
   static const ADD_MISSING_PARAMETER_REQUIRED = const FixKind(
       'ADD_MISSING_PARAMETER_REQUIRED', 30, "Add required parameter");
+  static const ADD_NE_NULL = const FixKind('ADD_NE_NULL', 50, "Add != null");
   static const ADD_PACKAGE_DEPENDENCY = const FixKind(
       'ADD_PACKAGE_DEPENDENCY', 50, "Add dependency on package '{0}'");
   static const ADD_PART_OF =
       const FixKind('ADD_PART_OF', 50, "Add 'part of' directive");
   static const ADD_SUPER_CONSTRUCTOR_INVOCATION = const FixKind(
       'ADD_SUPER_CONSTRUCTOR_INVOCATION',
       50,
       "Add super constructor {0} invocation");
   static const CHANGE_TO = const FixKind('CHANGE_TO', 49, "Change to '{0}'");
   static const CHANGE_TO_STATIC_ACCESS = const FixKind(
@@ skipping 67 matching lines @@
   static const USE_CONST = const FixKind('USE_CONST', 50, "Change to constant");
   static const USE_EFFECTIVE_INTEGER_DIVISION = const FixKind(
       'USE_EFFECTIVE_INTEGER_DIVISION',
       50,
       "Use effective integer division ~/");
   static const USE_EQ_EQ_NULL =
       const FixKind('USE_EQ_EQ_NULL', 50, "Use == null instead of 'is Null'");
   static const USE_NOT_EQ_NULL =
       const FixKind('USE_NOT_EQ_NULL', 50, "Use != null instead of 'is! Null'");
 }