[VB.NET]Conversion from type 'DBNull' to type 'integer' is not valid. แก้ยังไงดีครับ

    Private Sub cmdSave_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdSave.Click
        If txtEmployeeID.Text = "" Then
            MessageBox.Show("กรุณาระบุรหัสพนักงาน !!!", "ผลการตรวจสอบ", MessageBoxButtons.OK, MessageBoxIcon.Information)
            txtEmployeeID.Focus()
            Exit Sub
        End If

        If lsvDeviceList.Items.Count = 0 Then
            MessageBox.Show("กรุณาป้อนรายการยืมอุปกรณ์ !!!", "ผลการตรวจสอบ", MessageBoxButtons.OK, MessageBoxIcon.Information)
            txtSN.Focus()
            Exit Sub
        End If

        Dim sqlBorrow As String = ""
        Dim comBorrow As OleDbCommand = New OleDbCommand

        With Conn
            If .State = ConnectionState.Open Then .Close()
            .ConnectionString = strConn
            .Open()
        End With

        Try
            If MessageBox.Show("คุณต้องการบันทึกรายการยืมอุปกรณ์ ใช่หรือไม่?", "คำยืนยัน", MessageBoxButtons.YesNo, MessageBoxIcon.Question) = DialogResult.Yes Then

                AutoGenerateTranID()

                sqlBorrow = "INSERT INTO Borrow (TransID,EmployeeID,IsReturnAll) "
                sqlBorrow &= " VALUES('" & LastTransID & "',"
                sqlBorrow &= "'" & txtEmployeeID.Text & "',"
                sqlBorrow &= "0)"

                With comBorrow
                    .CommandType = CommandType.Text
                    .CommandText = sqlBorrow
                    .Connection = Conn
                    .ExecuteNonQuery()
                End With

                Dim i As Integer = 0
                Dim tmpSN As String = ""

                Dim sqlDevice As String = ""
                Dim tmpDeviceInShop As Integer = 0
                Dim tmpDeviceInBorrow As Integer = 0

                Dim tmpDeviceNum As Integer = 0
                Dim tmpDateNum As Integer = 0

                Dim tmpDateBorrow As Date
                Dim tmpDateReturn As Date

                tmpDateBorrow = Date.Now

                For i = 0 To lsvDeviceList.Items.Count - 1
                    sqlBorrow = "INSERT INTO BorrowDetail(TransID,SN,DateBorrow,"
                    sqlBorrow &= " ReturnDate,IsReturn)"
                    sqlBorrow &= " VALUES('" & LastTransID & "',"

                    tmpSN = lsvDeviceList.Items(i).SubItems(0).Text
                    tmpDeviceNum = CInt(lsvDeviceList.Items(i).SubItems(2).Text)
                    tmpDateNum = CInt(lsvDeviceList.Items(i).SubItems(3).Text)

                    sqlBorrow &= "'" & tmpSN & "',"
                    sqlBorrow &= "'" & tmpDateBorrow & "',"

                    tmpDateReturn = tmpDateBorrow.AddDays(tmpDateNum)

                    sqlBorrow &= "'" & tmpDateReturn & "',"
                    sqlBorrow &= "'0')"

                    With comBorrow
                        .CommandText = sqlBorrow
                        .ExecuteNonQuery()
                    End With

                    sqlDevice = "SELECT SN,DeviceInShop,DeviceInBorrow FROM Device"
                    sqlDevice &= " WHERE (SN='" & tmpSN & "')"

                    da.SelectCommand.CommandText = sqlDevice
                    da.Fill(ds, "Device")

                    tmpDeviceInShop = CInt(ds.Tables("Device").Rows(0).Item("DeviceInShop"))
                    tmpDeviceInBorrow = CInt(ds.Tables("Device").Rows(0).Item("DeviceInBorrow"))
                    ds.Tables("Device").Clear()

                    sqlBorrow = "UPDATE Device"
                    sqlBorrow &= " SET DeviceInShop=" & tmpDeviceInShop - tmpDeviceNum & ","
                    sqlBorrow &= " DeviceInBorrow=" & tmpDeviceInBorrow + tmpDeviceNum
                    sqlBorrow &= " WHERE (SN='" & tmpSN & "')"

                    With comBorrow
                        .CommandText = sqlBorrow
                        .ExecuteNonQuery()
                    End With
                Next


                MessageBox.Show("บันทึกรายการยืมอุปกรณ์เรียบร้อยแล้ว !!!", "ผลการทำงาน", MessageBoxButtons.OK, MessageBoxIcon.Information)


                ClearAllCustomerData()
                ClearAllDeviceData()
                lsvDeviceList.Items.Clear()


                cboDepartment.SelectedIndex = 0
                txtEmployeeID.Enabled = True
                txtEmployeeID.Focus()
            End If

        Catch ErrProcess As Exception
            MessageBox.Show("ไม่สามารถบันทึกรายการยืมอุปกรณ์ได้ เนื่องจาก " & ErrProcess.Message, "ข้อผิดพลาด", MessageBoxButtons.OK, MessageBoxIcon.Warning)
            Exit Sub
        End Try
    End Sub