my @part = (
    'http://example.net/app',
    ( 'admin'  ) x!! $is_admin_link,
    ( $subsite ) x!! defined $subsite,
    $mode,
    ( $id      ) x!! defined $id,
    ( $submode ) x!! defined $submode,
);

##</code><code>##

my @part = (
    'http://example.net/app',
    grep( $is_admin_link.    'admin' ),
    grep( defined($subsite), $subsite ),
    $mode,
    grep( defined($id),      $id      ),
    grep( defined($submode), $submode ),
);