Required fields for http_poller

[T3rm11]

The official documentation says that only urls is required. When I start Logstash I get the following error:

[2018-02-05T14:44:05,836][ERROR][logstash.inputs.http_poller] Missing a required setting for the http_poller input plugin:
input {
http_poller {
  schedule => # SETTING MISSING
  ...
 }
}