negation in the map directive of nginx

[libresco_27]

Thanks Francis for your response.

I tried the approach you suggested and it still doesn't seem to work. 
This is what I am doing right now :-

limit_req_zone $default_client_id zone=sample_zone:50k rate=3r/m sync;
map $client_id $default_client_id {
        ZZZZZ "";
        $client_id $client_id;
}

When I try to hit the gateway with ZZZZ client_id, it still limits the
requests according to 3rpm configuration. Am I doing this wrong?

(PS - I'm pretty new to nginx, sorry if I'm asking dumb questions:) )

Posted at Nginx Forum: https://forum.nginx.org/read.php?2,295157,295170#msg-295170