public void XmlLoadTest()
{
DataSet ds;
ds = Create();
DataTable dt = ds.Tables[0];
DataRow dr = dt.NewRow();
dr["CustName"] = DBNull.Value;
dr["Type"] = typeof(DBNull);
dt.Rows.Add(dr);
ds.WriteXml(_tempFile, XmlWriteMode.DiffGram);
ds = Create();
ds.ReadXml(_tempFile, XmlReadMode.DiffGram);
}