Crash logstash after updating from 5.3 to 5.5

Elastic Stack Logstash
4

Crashes if I apply such a filter

filter {
  if [type] == "postfix-events" {
        grok {
            patterns_dir => ["/etc/logstash/patterns.d"]
            match => { "message" => ["%{PF}"] }
        }
        date {
            match => [ "timestamp", "MMM dd HH:mm:ss" ]
        }
    }
    # monitor metrics and health of logstash
    metrics {
        meter => [ "events" ]
        add_tag => "metric"
    }
}

and I have fields with dots.
But in version 5.3, this did not cause a crash.