Null reference exception in Transaction

Question

Im having problem with a null reference exception while executing the code

trans.Rollback() . Kindly help ASAP.

Thanx in Advance.

FYI:

1. Dim trans As OleDbTransaction
2.  
3.         Try
4.             trans = con.BeginTransaction
5.             If con.State = ConnectionState.Closed Then
6.                 con.Open()
7.             End If
8. Dim cmd_inward As OleDbCommand = New OleDbCommand("Insert into inward_entry(in_date,product_name,batch_no,Pack,type, qty,Description,Mfd_Company,Exp_Date,Purchased_price,MRP) values (#" & Todate & "#,'" & Prd_nm & "', '" & Prd_batch & "','" & Prd_pack & "', '" & prd_type & "','" & item_Qty & "', '" & prd_description & "','" & Mfd_By & "','" & exp_dt & "', '" & Pur_prc & "','" & Prd_MRP & "')", con)
9.             cmd_inward.Transaction = trans
10.             cmd_inward.ExecuteNonQuery()
11.             Dim cmd_pur_mast As OleDbCommand = New OleDbCommand("insert into purchase_master (purchase_date,product_name,item_pack,Batch_no,product_purchase_price,item_qty) values (#" & Todate & "#, '" & Prd_nm & "','" & Prd_pack & "','" & Prd_batch & "', '" & Pur_prc & "','" & item_Qty & "')", con)
12.             cmd_pur_mast.Transaction = trans
13.             cmd_pur_mast.ExecuteNonQuery()
14.             Dim cmd_prd_mast As OleDbCommand = New OleDbCommand("insert into product_master(product_name, item_pack,product_manufacturer,product_description) values ('" & Prd_nm & "','" & Prd_pack & "','" & Mfd_By & "','" & prd_description & "')", con)
15.             cmd_prd_mast.Transaction = trans
16.             cmd_prd_mast.ExecuteNonQuery()
17. Dim cmd_select_warehouse As OleDbCommand = New OleDbCommand("Select * from warehouse_master where product_batch_no='" & Prd_batch & "' and  product_name='" & Prd_nm & "' and item_pack='" & Prd_pack & "' ", con)
18.             Dim rdr As OleDbDataReader
19.             rdr = cmd_select_warehouse.ExecuteReader()
20. If rdr.Read() = False Then
21. Dim cmd_insert As OleDbCommand = New OleDbCommand("Insert into warehouse_master(product_batch_no, product_manufacturer, product_name,item_pack, available_qty,product_exp_date,product_MRP) values('" & Prd_batch & "','" & Mfd_By & "','" & Prd_nm & "', '" & Prd_pack & "','" & item_Qty & "', '" & exp_dt & "', '" & Prd_MRP & "')", con)
22.                 cmd_insert.Transaction = trans
23.                 cmd_insert.ExecuteNonQuery()
24.  
25.             Else
26.                 MessageBox.Show("data")
27.                 Dim cmd_update As OleDbCommand = New OleDbCommand("Update warehouse_master set available_qty= available_qty + '" & item_Qty & "' where product_batch_no = '" & Prd_batch & "' and product_Name = '" & Prd_nm & "' and Item_pack= '" & Prd_pack & "'", con)
28.                 cmd_update.Transaction = trans
29.                 cmd_update.ExecuteNonQuery()
30.  End If
31.  
32.             trans.Commit()
33.         Catch ex As Exception
34.  trans.Rollback()
35.  
36.             MessageBox.Show("Transaction Rolled Back")
37.         Finally
38.             con.Close()
39.         End Try
40.