samba-tool dns add 172.31.9.161 s4xdom.base . NS mydns.org.
gives a no memory error, while
samba-tool dns add 172.31.9.161 s4xdom.base @ NS mydns.org.
works fine.

A Windows server allows both.

dns_split_node_name() return NULL for node_name == '.'
called from dnsserver_update_record()


        /* If node_name is @ or zone name, dns record is @ */
        if (strcmp(node_name, "@") == 0 || strcasecmp(node_name, z->name) == 0) {
                name = talloc_strdup(tmp_ctx, "@");
        } else {
                name = dns_split_node_name(tmp_ctx, node_name, z->name);
        }
        W_ERROR_HAVE_NO_MEMORY_AND_FREE(name, tmp_ctx);

Maybe we should have an additional strcmp(node_name, '.') == 0
for the name = talloc_strdup(tmp_ctx, "@") case.