Logstash Syslog input crashes with a malformed request

[Roberto_1 (Roberto)]

Hello,
I see that my Logstash, set with a simply Syslog input configuration, crash anytime I test the listening port with Netcat.

Below my Logstash Input configuration.

input {
  syslog {
    port => 5000
  }
}
output {
    file {
        path => "/data/logs_dir/log-%{+YYYY-MM-dd}.txt"
        codec => rubydebug
    }
 }

When I connect to that port with Netcat, and I try to send some raw data ("test" string, for example), Logstash crashes. Following the crash error log

[2018-11-13T11:11:21,388][ERROR][org.logstash.Logstash    ] java.lang.IllegalStateException: Logstash stopped processing because of an error: (SystemExit) exit

I know that sending a custom string via Netcat is not a Syslog, but how can I avoid that, for a malformed request sent to Logstash, the service crashes?

Thank a lot.

Bye,
Roberto