- my $mb = cmdoutput @git, qw(merge-base), $ancestor, $child;
- return rev_parse($mb) eq rev_parse($ancestor);
+ my @cmd = (@git, qw(merge-base), $ancestor, $child);
+ my $mb = cmdoutput_errok @cmd;
+ if (defined $mb) {
+ return rev_parse($mb) eq rev_parse($ancestor);
+ } else {
+ $?==256 or failedcmd @cmd;
+ return 0;
+ }