Unexpected end of JSON input

I follow https://blog.containo.us/traefik-2-0-docker-101-fc2893944b9d.
I create a new acme.json file (by nano), change its permissions with 600 and start container.
But I get flags."time="2019-10-17T04:45:08Z" level=error msg="Unable to add ACME provider to the providers list: unable to get ACME account: unexpected end of JSON input"
So I can not reach the dashboard, and another website.

Traefik version : 2.0.2

I resolved this error by changing the contents of acme.json from '' to {}.