anchor.diff:    }
     
     isDirty() {
  -    return !_dirtiFields.isEmpty();
  +    return !_dirtyFields.isEmpty();
     }
     
     
  
positive.code: 
  class BasePersistentObject {
    LinkedHashMap map;
    Set<String> _dirtiFields;
    Map<String,Dynamic> _compoundProperties;
    bool saveOnUpdate = false;
    BasePersistentObject() {
  
negative.code:   }  
    
    void setDirty(String fieldName) {
      if (_dirtyFields === null){
        return;
      }
      _dirtyFields.add(fieldName);
    }
    
    void clearDirtyStatus() {
      _dirtyFields.clear();
    }
    
    void onValueChanging(String fieldName, newValue) {
  