(5.x) Filter config fails/terminates silently

[strarsis]

With Logstash 5.x, filter configuration in conf.d fails silently and Logstash terminates without further notice, it worked in Logstash prior to 5.x. Input + output configuration also exists and Logstash runs fine and without terminating when the nginx filter configuration has been removed.

Sending Logstash logs to /var/log/logstash which is now configured via log4j2.properties.
(exits)

Checking the configuration using --config.test_and_exit:

Sending Logstash logs to /var/log/logstash which is now configured via log4j2.properties.
Configuration OK
(exits)

Logstash main configuartion file (without commented out lines):

path.data: /var/lib/logstash
path.config: /etc/logstash/conf.d
path.logs: /var/log/logstash

Filter configuration file:

filter {
  if [type] == "nginx-access" {
    grok {
      patterns_dir => [ "/etc/logstash/pattern" ]
      match        => { "message" => "%{NGINXACCESS}" }
    }
  }
}

If there is an issue with the filter or used pattern, Logstash should log about it, also the configuration test should instead fail, so this can be considered as a bug?

Edit: The patterns directory (/etc/logstash/pattern) was not present, still an error should be logged.