Today I tried to change the current working directory using some absolute path name on on of my windows build agents. Unfortunately it reports a NullPointerException instead
I tried both

dir('c:\\')

as well as

dir('c:/')

.

I tried as well the following - which won't give me a NullPointerException but still won't work:

dir('c:')
dir('//?/c:/')
dir('\\\\?\\c:\\')

Hoever if I use

dir('\\')

it works just fine.
Unfortunately until now I don't see a possibility to change to a different drive using that approach.
E.g. Jenkins workspace is located on d: while I want to change to a directory located on c: drive.