bugfix: send empty json object on 404 rather than nil

sending nothing was keeping the connection alive.

lib/nickserver/couch_db/response.rb

@@ -17,7 +17,11 @@ module Nickserver::CouchDB
     end
 
     def content
-      key_response if ok? && !empty?
+      if ok? && !empty?
+        key_response
+      else
+        not_found_response
+      end
     end
 
     protected
@@ -26,6 +30,10 @@ module Nickserver::CouchDB
       format address: nick.to_s, openpgp: key
     end
 
+    def not_found_response
+      format({})
+    end
+
     def format(response)
       response.to_json
     end