🚀 go-pugleaf

Hi collegues!
I use Builder4 in multi-tier application.
Trying to set NULL in memo field, I've found that
function Param->AssignFieldValue can't do it!
Not null - please, but when I clear field on client
side and use standart event on DataSetProvider in server,
that field in table has old value. Anybody knows is it bug
or I am big fool? (See the code below)

void __fastcall TDBServer::GridConfigProviderBeforeUpdateRecord(
      TObject *Sender, TDataSet *SourceDS, TClientDataSet *DeltaDS,
      TUpdateKind UpdateKind, bool &Applied)
{
   TQuery * Query = UpdateSQLGrid->Query[UpdateKind];
   Query->SessionName=MtrDatabase->SessionName;
   Query->DatabaseName=MtrDatabase->DatabaseName;
   //for(int i=0; i < 9; i++)
   for(int i=0; i < SourceDS->Fields->Count; i++)
   {
     AnsiString Name=SourceDS->Fields->Fields[i]->FieldName;
     TParam * Param=Query->Params->FindParam(Name);
     if(Param)
     {
       Variant var = DeltaDS->Fields->Fields[i]->NewValue;
       Variant old = DeltaDS->Fields->Fields[i]->OldValue;
       if(var.IsEmpty())    // || var.IsNull())
       Param->AssignFieldValue(DeltaDS->Fields->Fields[i], old);
       else
       Param->AssignFieldValue(DeltaDS->Fields->Fields[i], var);
     }
     Param=Query->Params->FindParam("OLD_"+Name);
     if(Param)  
     {
       Param->AssignFieldValue(DeltaDS->Fields->Fields[i], DeltaDS->Fields->Fields[i]->OldValue);
     }
   }
   Query->Prepare();
   Query->ExecSQL();
   Applied=true;
}