Quoting from the upstream patch:
Jan Alexander Steffens reported that when `rebase.abbreviateCommands'
is set, the merge backend fails to fast forward. This is because the
backend generates a todo list with only a `noop', and since this
command has no abbreviated form, it is replaced by a comment mark.
The sequencer then interprets it as if there is nothing to do, and
fails.
References:
https://github.com/git/git/commit/68e7090f31https://lore.kernel.org/git/9b4bc756764d87c9f34c11e6ec2fc6482f531805.camel@gmail.com/
