sub _run_cmd {
my $out;
- my $pid = open3( undef, $out, undef, $^X, shellwords($ENV{HARNESS_PERL_SWITCHES}), @_ );
+ my $pid = open3( undef, $out, undef, $^X, shellwords($ENV{HARNESS_PERL_SWITCHES}||''), @_ );
my $res = do { local $/; <$out> };
waitpid($pid, 0);
$res;