Difference between the Length attribute in the Microsoft. VisualBasic. Len function and the system. string class

Environment: vs2003, vs.net
Generally, I want to evaluate the length of a string. There are two methods.
1 is the Microsoft. VisualBasic. Len function; 2 is the Length attribute in the system. string class.
The two functions are similar, but when the string is nothing (C # Is null), the first method returns 0, and the second method returns an error.
As follows:Code:

1 Dim I As Int16
2
3 Dim Stra As   String
4 Stra =   Nothing
5 I = Microsoft. VisualBasic. Len (stra) 'I is 0
6 I = Stra. length' throws an nullreferenceexception
7

Use reflector to check the Microsoft. VisualBasic. Len function. The original function is written as follows:

1 Public   Shared   Function Len () Function   Len ( Byval Expression As   String ) As   Integer
2 If (Expression Is   Nothing ) Then
3 Return   0
4 End   If
5 Return Expression. Length
6 End Function

To use the Length attribute in the system. string class to implement similar functions, You can manually add segmentsProgramTo determine the null value of the string.

If Stra Is   Nothing   Then
I =   0
Else
I = Stra. Length
End   If