how slove this error:UpdateParameters

how to slove this problam

 
  if (e.CommandName == "Update")
        {
            GridViewRow gvrow = (GridViewRow)((ImageButton)e.CommandSource).NamingContainer;
            TextBox txtbarndFaName = (TextBox)gvrow.FindControl("TFBrandFaNameedit");
            TextBox txtbarndEnName = (TextBox)gvrow.FindControl("TFBrandEnNameedit");
            DropDownList txttypepartEnName = (DropDownList)gvrow.FindControl("DDTypehardware");
            int a = int.Parse(txttypepartEnName.SelectedValue);
            SqlDupdate.UpdateParameters["FBrandFaName"].DefaultValue = txtbarndFaName.Text;
            SqlDupdate.UpdateParameters["FBrandEnName"].DefaultValue = txtbarndEnName.Text;
         SqlDupdate.UpdateParameters["FPartCatID"].DefaultValue = txttypepartEnName.SelectedValue.ToString();
                
            SqlDupdate.Update();      
        }

 
this error:
System.NullReferenceException: Object reference not set to an instance of an object.
 
DropDownList txttypepartEnName = (DropDownList)row.FindControl("DDTypehardware
 
the type filed db is smallint.
how to convert SqlDupdate.UpdateParameters["FPartCatID"].DefaultValue = txttypepartEnName.SelectedValue.ToString();
 
to int.