Log Socket Response always displays undefined in artillery.io

Question

Here is my yaml file.

config:
  target: "http://localhost:3000"
  phases:
      - duration: 5 
        arrivalRate: 1
  socketio:
      transports: ["websocket"]

scenarios:
  - name: "Emit an event"
    engine: socketio
    flow:
      - emit:
          channel: "chat-message"
          data: { "msg": "fooBar2" }
          response:
            channel: "chat-message"
            capture: 
              json: "$"
              as: "res"
      - log: "{{res}}"

While running it just logs undefined. What am i doing wrong here?