anchor.diff:      _contextMessages = contextMessages;
     }
   
  -  List<DiagnosticMessage> get contextMessages => _contextMessages ?? const [];
  +  List<DiagnosticMessage> get contextMessages => _contextMessages;
   
     /**
      * Return the template used to create the correction to be displayed for this
  
positive.code:    * [contextMessages] are provided, they will be recorded with the error.
     */
    AnalysisError(this.source, int offset, int length, this.errorCode,
        [List<Object> arguments, List<DiagnosticMessage> contextMessages]) {
      String message = formatList(errorCode.message, arguments);
      String correctionTemplate = errorCode.correction;
      if (correctionTemplate != null) {
  
negative.code:    */
    AnalysisError.forValues(this.source, int offset, int length, this.errorCode,
        String message, this._correction,
        {List<DiagnosticMessage> contextMessages = const []}) {
      _problemMessage = new DiagnosticMessageImpl(
          filePath: source?.fullName,
          length: length,
  