don't execute n1ql request with key params at nil

[giallon]

If we have Mission class

class Mission
   n1ql: by_route, emit_key: route_id
end

and we call by_route with key params at nil

Mission.by_route(key: nil).last

then this method will build this request N1QL : SELECT raw meta().id FROM default WHERE type=“mission“ ORDER BY route_id asc,meta().id asc

It's very dangerous. Request N1QL is used by association (has_many)