Jeremy Morton [off-list ref] writes:
I've noticed that when you're merging and there is a 'both added'
merge conflict, git creates the .LOCAL and .REMOTE files for the
merge, but not the .BASE file.
Strictly speaking, git doesn't, but I think mergetool may.
You may find this thread interesting:
http://thread.gmane.org/gmane.comp.version-control.git/188776/focus=188867
which resulted in ec245ba (mergetool: Provide an empty file when needed,
2012-01-19); that change is in v1.7.9.1 and upwards IIRC.