I am not sure why VB makes everything such a pain. I have a fields which stores the date and time in the format required to store in MySQL database
Dim AppDate As String = String.Empty
If Not String.IsNullOrEmpty(Me.AppDate.Text.Trim) Then
AppDate = Format(CDate(Me.AppDate.Text), "yyyy-MM-dd h:mm:ss")
//Need to assign a null value to AppDate
AppDate = Nothing should work, you could also use DateTime.MinValue and update your business logic to treat it appropriately.