[02/03] how to send an empty text box value to database

[puresmile]

i've created a web page taking inputs from user. There are some options for users which are optional. but when it is left empty; an error comes saying format of string is not correct. how can i do this? I've put "fieldvalidator" only for compulsory input. I'm inserting data in sql server 2000. here is my code

Sub SaveCustomer(ByVal s As Object, ByVal e As EventArgs) Handles btnSave.Click
 
        If Page.IsValid Then
 
            Dim objCustomer As New BusinessLogicLayer.MyCustomers
 
             objCustomer.RecordId = CType(txtRecordId.Text, Long)
            objCustomer.CustomerNo = CType(txtCustomerNo.Text, Long)
            objCustomer.RecordDate = CType(CurrentDate.Text, DateTime)
            objCustomer.Customername = txtCustomerName.Text
            objCustomer.CustomerCompanyName = txtCompanyName.Text
            objCustomer.CustomerBillingAddress = txtBillingAddress.Text
            objCustomer.CustomerTelePhoneNo = CType(txtTelePh.Text, Long)
          
 
           If Not objCustomer.Save() Then
              lblError.Text = "Could not save Customer"
 
           End If
        End If
    End Sub 'SaveUser

while i've declared variables in "MyCustomers" class as. here i've initialized those variables which are optional

Private _CustomerNo As Long = 0
        Private _RecordId As Long
        Private _RecDate As DateTime
 
        Private _Customername As String
        Private _CustomerCompanyName As String = ""
        Private _CustomerBillingAddress As String
        Private _CustomerTelePhoneNo As Long