... also it's a prototype.
filter => sub { 1 },
empty => undef,
);
-sub _env_list_value(%@) {
+sub _env_list_value {
my $options = shift;
die(sprintf "unknown option '$_' at %s line %u\n", (caller)[1..2])
for grep { !exists $ENV_LIST_VALUE_DEFAULTS{$_} } keys %$options;