surprising error message in parse_opt_with_commit

When I typed 'git branch --contains efabdfb' on a machine today, I was surprised to receive this error message: "error: malformed object name efabdfb"

I would have expected instead to receive the message: "no such commit: efabdfb".

I went hunting through the source code and found the origination point of the error:

/parse-options.c
 610 int parse_opt_with_commit(const struct option *opt, const char
*arg, int unset)
 611 {
 612 	unsigned char sha1[20];
 613 	struct commit *commit;
 614
 615 	if (!arg)
 616 		return -1;
 617 	if (get_sha1(arg, sha1))
 618 		return error("malformed object name %s", arg);
 619 	commit = lookup_commit_reference(sha1);
 620 	if (!commit)
 621 		return error("no such commit %s", arg);
 622 	commit_list_insert(commit, opt->value);
 623 	return 0;
 624 }

It appears the get_sha1 call is returning true, causing the 'malformed object name' error to be returned. However, it seems that ideally since efabdfb is not malformed (it would be a valid ref if it existed), the execution path should continue to line 619, receive no commit, and fail on 621.

Am I off base here?