Why does GetName in System.Reflection.Assembly appear to throw a NotImplementedException when decompiled?

While debugging an issue I was digging in to mscorlib and specifically at GetName() in System.Reflection.Assembly.

Looking at the code for the method in dotPeek and also on reference source the code for GetName() seems to have nothing in it and throws a not implemented exception (see image).

Can anyone explain why this appears to throw an exception, but using a line of code such as typeof(object).GetTypeInfo().Assembly.GetName().Version.ToString() returns the correct version of the DLL?