There seem to be an issue with the automatic installation (which is a great feature for nodes).

Below are my Jenkins global settings on Windows:

Path to Git executable: C:\Jenkins Tools\Git

[X] Install automatically:
Label:
Download URL for binary archive: file:///C:/Repo/PortableGit-1.7.8-preview20111206.zip
Subdirectory of extracted archive: bin\git.exe

First, it's weird to set "Path to Git executable" as being the folder, but else the automatic install won't extract in the proper place.

When the folder does not exist, it seem to correctly extract it and call "C:\Jenkins Tools\Git\bin\git.exe" (seems at least).

When the folder does exist, it tries to call 'null' and fails.

Note: I didn't set "Git" "Tool Locations" for Git on any node nor globally. Also having that tool location globally additional to the "Path to Git executable" is confusing.