strcmp_maybe_null
if (strcmp_maybe_null(a->listen_host, b->listen_host) == 0)
if (strcmp_maybe_null(a->listen_path, b->listen_path) == 0)
if (strcmp_maybe_null(a->connect_host, b->connect_host) == 0)
if (strcmp_maybe_null(a->connect_path, b->connect_path) == 0)