anchor.diff:      Token token = scanString(parserSource).tokens;
       while (!token.isEof) {
         if (token.isIdentifier) {
  -        String fastaErrorCode;
  +        String? fastaErrorCode;
           String lexeme = token.lexeme;
           if (lexeme.length > 7) {
             if (lexeme.startsWith('message')) {
  
positive.code:           untranslatedFastaErrorCodes.add(fastaErrorCode);
          }
        }
        token = token.next;
      }
      if (untranslatedFastaErrorCodes.isNotEmpty) {
        print('');
  
negative.code: /// This file contains code to generate scanner and parser message
  /// based on the information in pkg/front_end/messages.yaml.
  ///
  