anchor.diff:  
       property Key : TListDatumKey read FKey;
       property Description : string read FDescription write FDescription;
  -    property Value : TNullableValue read FValue;
     end;
   
   
  
positive.code: 
  function TListDataProvider.GetKeyFieldName: String;
  begin
    Result := TListDatum.FLD_ID;
  end;
  
  procedure TListDataProvider.GetMinimumFields(aFieldsForLookup: TStringList);
  
negative.code: 
  class procedure TListDatum.FillVirtualFieldDefs(aFieldDefs: TmVirtualFieldDefs; const aPrefix: String);
  begin
    with aFieldDefs.AddFieldDef do
    begin
      Name := aPrefix + FLD_DESCRIPTION;
  