How to remove untranslated trap event from logstash?

i have defined a lot of yaml for snmp trap that i want , and put these yaml in my mib directory(specificmibs), and defined the mib directory in my conf as follows,
yamlmibdir => "/opt/logstash/vendor/bundle/jruby/1.9/gems/snmp-1.2.0/data/ruby/snmp/specificmibs"

but how to remove the event when the mib can't found in yamlmibdir ?

How can I make logstash drop it?

This question is almost word for word the same as [drop] the same message. Are you posting using multiple accounts?

What does a message that you want to drop look like and what does a message you want to keep look like?