msg::tests::serialize_request_with_null_params fails

[Rutherther]

This test fails with this error:

assertion `left == right` failed
  left: "{\"id\":3,\"method\":\"shutdown\"}"
 right: "{\"id\":3,\"method\":\"shutdown\",\"request_tick\":\"\"}"

In the actual value there is request_tick. I would submit a PR, but I am not sure if request_tick should be there - so whether it's error of the test or error of the serialization.