anchor.diff:          );
   
     @override
  -  dynamic getValue(FieldReference dataObject) =>
  +  String getValue(FieldReference dataObject) =>
         dataObject.isEmptyReference || dataObject.isSentinelReference
             ? ''
  -          : dataObject.value;
  +          : dataObject.value ?? '';
   
     @override
     String getDisplayValue(FieldReference dataObject) {
  
positive.code: 
    @override
    int compare(FieldReference a, FieldReference b) {
      final Comparable valueA = getValue(a);
      final Comparable valueB = getValue(b);
      return valueA.compareTo(valueB);
    }
  
  
negative.code:         );
  
    @override
    String getValue(FieldReference dataObject) =>
        dataObject.isEmptyReference ? '' : dataObject.name;
  
    @override
  