Set the status code to 400 when invalid query params are sent

lib/nbi.coffee

@@ -341,8 +341,10 @@ listener = (request, response) ->
         if urlParts.query.query?
           try
             q = JSON.parse(urlParts.query.query)
-          catch e
-            q = {}
+          catch err
+            response.writeHead(400)
+            response.end(err.toString())
+            return
         else
           q = {}
         q = query.expand(q, aliases) if collectionName is 'devices'