support for sending timestamp to zabbix

This isn't working yet but wanted to get your feedback about what I might be doing wrong (as well as overall thoughts on the feature). I am getting an exception around line 110 as follows:

NameError: uninitialized constant LogStash::Outputs::Zabbix::Nil
  const_missing at org/jruby/RubyModule.java:2690
        receive at /opt/itson-elk/logstash/lib/logstash/outputs/zabbix.rb:110
         handle at /opt/itson-elk/logstash/lib/logstash/outputs/base.rb:86
     initialize at (eval):76
           call at org/jruby/RubyProc.java:271
         output at /opt/itson-elk/logstash/lib/logstash/pipeline.rb:266
   outputworker at /opt/itson-elk/logstash/lib/logstash/pipeline.rb:225
  start_outputs at /opt/itson-elk/logstash/lib/logstash/pipeline.rb:152

I suspect need to do something different to add a new field. Anything you can point me to is much appreciated. Thanks