Insert Null In A Numeric Field

I need to insert a null valvue when the user does not impute any text.

here is my code

If cell_phone.Text = "" Then

cell_phone.Text = "dbnull.value"

End IfDim mySqlConnection As New SqlConnection

mySqlConnection.ConnectionString = ConfigurationManager.ConnectionStrings("Call_ListConnectionString").ConnectionString

Dim strSQL As String = "INSERT INTO Employees(Clock_ID, Last_Name, First_Name, Cell_Phone, Home_Phone, Work_Phone, Email, Primary_Day_Phone, Primary_Night_Phone, Blackberry_Number) VALUES ('" & clock_id.Text & "','" & last_name.Text & "','" & first_name.Text & "','" & work_phone.Text & "','" & home_phone.Text & "','" & cell_phone.Text & "','" & email.Text & "','" & prime_day_lst.SelectedValue & "','" & prime_night_lst.SelectedValue & "','" & blackberry.Text & "')"Dim mySqlCommand As New SqlCommand(strSQL, mySqlConnection)

mySqlConnection.Open()

mySqlCommand.ExecuteNonQuery()

mySqlConnection.Close()

THanks

Mike