主题：用于判断是否包括Nothing返回假而不报错

Dim el_dn As String = Nothing
Output.Show(DataTables.Contains(el_dn))

Dim arr As New List(Of String)
Output.Show(arr.Contains(el_dn))

Dim Str1 As String = "I like foxtable"
Output.Show(Str1.Contains(el_dn))