yes, i use vb.net and i agree with you . Because i go to query builder test is no problem.
Do you know how to check the @lineno parameter store what value and adjust this or any same method to set the null?

Actually, my real problem is i have datagridview(DataGridViewComboBoxColumn) and databindings. I want to set the datagirdview.row(0).cell(0).value = DBNull.Value.
But execute this statement after i see the debug mode datagirdview.row(0).cell(0).value change to " " (empty string)

If the datagirdview.row(0).cell(0).value is empty string and save to database will error, because the empty string not include DataGridViewComboBoxColumn value.
So i need to save the record before and adjust the @lineno or datagirdview.row(0).cell(0).value to dbnull value.