Replace data value from dataset which is coming from database

dsProductionDocumentList = objProduction.GetProductionDocumentListByProductionStep((int)structures.ProductionStep.Washing);
foreach (DataRow dr in dsProductionDocumentList.Tables[0].Rows)
{
if (dr["Scrap_Qty"] == DBNull.Value Convert.ToInt32(dr["Scrap_Qty"]) == 0)
{
dr["Scrap_Qty"]=string.Empty;
}
}