Logstash error "exception in filterworker"

Hi,

Does someone encountered the following error before:

Jul 28 08:56:32 syslog1-ctr logstash: {:timestamp=>"2015-07-28T08:56:32.481000+0200", :message=>"Exception in filterworker", "exception"=>#<TypeError: can't dup NilClass>, "backtrace"=>["org/jruby/RubyKernel.java:2064:in dup'", "file:/opt/logstash/vendor/jar/jruby-complete-1.7.11.jar!/META-INF/jruby.home/lib/ruby/1.9/date/format.rb:833:in_parse'", "file:/opt/logstash/vendor/jar/jruby-complete-1.7.11.jar!/META-INF/jruby.home/lib/ruby/1.9/time.rb:265:in parse'", "(ruby filter code):1:inregister'", "org/jruby/RubyProc.java:271:in call'", "/opt/logstash/lib/logstash/filters/ruby.rb:38:infilter'", "(eval):310:in initialize'", "org/jruby/RubyProc.java:271:incall'", "/opt/logstash/lib/logstash/pipeline.rb:262:in filter'", "/opt/logstash/lib/logstash/pipeline.rb:203:infilterworker'", "/opt/logstash/lib/logstash/pipeline.rb:143:in start_filters'"], :level=>:error} Jul 28 11:44:55 syslog1-ctr logstash: {:timestamp=>"2015-07-28T11:44:55.666000+0200", :message=>"Exception in filterworker", "exception"=>#<TypeError: can't dup NilClass>, "backtrace"=>["org/jruby/RubyKernel.java:2064:indup'", "file:/opt/logstash/vendor/jar/jruby-complete-1.7.11.jar!/META-INF/jruby.home/lib/ruby/1.9/date/format.rb:833:in _parse'", "file:/opt/logstash/vendor/jar/jruby-complete-1.7.11.jar!/META-INF/jruby.home/lib/ruby/1.9/time.rb:265:inparse'", "(ruby filter code):1:in register'", "org/jruby/RubyProc.java:271:incall'", "/opt/logstash/lib/logstash/filters/ruby.rb:38:in filter'", "(eval):307:ininitialize'", "org/jruby/RubyProc.java:271:in call'", "/opt/logstash/lib/logstash/pipeline.rb:262:infilter'", "/opt/logstash/lib/logstash/pipeline.rb:203:in filterworker'", "/opt/logstash/lib/logstash/pipeline.rb:143:instart_filters'"], :level=>:error}

If, yes, what it is and how can I solve it, please ?

You seem to have a ruby filter that doesn't respond well to certain events.