public Object getExtraArg(String key) {
    if (extraArgs.has(key)) {
      return null;
    }

    try {
      return extraArgs.get(key);
    } catch (JSONException e) {
      return null;
    }
  }
The port at which the server should listen.
selendroid-server/src/main/java/io/selendroid/server/InstrumentationArguments.java