Using really empty start prefixes for git-format-patch numbered patches?

Hi,

I'm trying to generate numbered patches using git-format-patch such
that I get e.g. [1/2] instead of [PATCH 1/2]

However, if I use an empty string as prefix, for instance in

git-format-patch --subject-prefix="" -2

an extraneous space is inserted, and I get [ 1/2] instead of desired
[1/2] in the Subject line

(I also tried using a single backspace char as prefix, but that didn't
change anything, as might have been expected)

Is there a way to get rid of this space? IMO the space should only be
added if the prefix is non-empty

Frédéric Delanoy