anchor.diff:  
   /// A bazel worker loop that can compute full or summary kernel files.
   class KernelWorker extends AsyncWorkerLoop {
  -  fe.InitializedCompilerState previousState;
  +  fe.InitializedCompilerState? previousState;
   
     /// If [sendPort] is provided it is used for bazel worker communication
     /// instead of stdin/stdout.
  -  KernelWorker({SendPort sendPort})
  +  KernelWorker({SendPort? sendPort})
         : super(
               connection: sendPort == null
                   ? null
  
positive.code: // Copyright (c) 2017, 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.
  
  // @dart = 2.8
  
  /// A tool that invokes the CFE to compute kernel summary files.
  ///
  
negative.code:     var outputBuffer = new StringBuffer();
      var response = new WorkResponse()..exitCode = 0;
      try {
        fe.InitializedCompilerState? previousStateToPass;
        if (request.arguments.contains("--reuse-compiler-result")) {
          previousStateToPass = previousState;
        } else {
  