anchor.diff:  
   import 'package:crypto/crypto.dart';
   import 'package:github/github.dart';
  +import 'package:github/hooks.dart';
   import 'package:meta/meta.dart';
  -import 'package:github/hooks.dart';
   
   import '../datastore/cocoon_config.dart';
   import '../model/appengine/service_account_info.dart';
  
positive.code:   }
  
    Future<void> _handlePullRequest(String rawRequest) async {
      // ignore: undefined_class
      final PullRequestEvent pullRequestEvent =
          await _getPullRequestEvent(rawRequest);
      if (pullRequestEvent == null) {
        throw const BadRequestException('Expected pull request event.');
      }
      // ignore: invalid_assignment
      final String eventAction = pullRequestEvent.action;
      // ignore: invalid_assignment
      final PullRequest pr = pullRequestEvent.pullRequest;
  
      // See the API reference:
  
negative.code:     return bodySignature == signature;
    }
  
    Future<PullRequestEvent> _getPullRequestEvent(String request) async {
      if (request == null) {
        return null;
      }
      try {
        return PullRequestEvent.fromJson(
            json.decode(request) as Map<String, dynamic>);
      } on FormatException {
  