Quoting Linus Torvalds [off-list ref]:
Note that git-patch-id will happily take a patch without the commit ID at
the head, it just won't have a commit ID to match it up with. For such
patches it will just spit it out with an all-zero commit-object-name.
And that's very much by design.
[snip]
OK, if it's by design, I'll fix gitk only.
I understand the default behavior of git-diff-tree won't change, so I'll simply
strip the first line.
--
Regards,
Pavel Roskin