Testing for Null in Stored Proc Return Value

Private Function CreInvData(ByVal sStoredProcName As String) As Long
Dim oCmd As New ADODB.Command
Dim oParam As ADODB.Parameter
Set oCmd.ActiveConnection = invConn
oCmd.CommandText = sStoredProcName
oCmd.CommandType = adCmdStoredProc
oCmd.Parameters.Append oCmd.CreateParameter("clCode", adVarChar, adParamInput, 4, sClCode)
oCmd.Parameters.Append oCmd.CreateParameter("chgRate", adInteger, adParamInput, , i)
oCmd.Parameters.Append oCmd.CreateParameter("clStRate", adCurrency, adParamInput, , clStRate)
oCmd.Parameters.Append oCmd.CreateParameter("W", adVarChar, adParamInput, 1, W)
oCmd.Parameters.Append oCmd.CreateParameter("Total", adCurrency, adParamReturnValue)
oCmd.Execute
If oCmd.Parameters("Total") = vbNull Then
    total = 0
Else
    total = oCmd.Parameters("Total")
End If