die "v2 not supported: $@\n" if $@;
my $opt = $self->{-creat_opt};
my $v2w = PublicInbox::V2Writable->new($self, $opt);
- $v2w->{parallel} = $parallel;
+ $v2w->{parallel} = $parallel if defined $parallel;
$v2w;
} elsif ($v == 1) {
my @arg = (undef, undef, undef, $self);