Visual Basic 运行时和 .NET Framework 在处理字符串时，对于 Nothing 的评估方式有所不同。
Visual Basic 运行时和 .NET Framework
请看下面的示例：
Dim MyString As String = "This is my string"
Dim stringLength As Integer
' Explicitly set the string to Nothing.
MyString = Nothing
' stringLength = 0
stringLength = Len(MyString)
' This line, however, causes an exception to be thrown.
stringLength = MyString.Length
Visual Basic 运行时通常将 Nothing 评估为空字符串 ("")。 而 .NET Framework 不会这样求值，只要尝试对 Nothing 执行字符串操作，它就会引发异常。
