Have the below error please help to solve it.
[2019-03-11T12:15:39,040][FATAL][logstash.runner ] An unexpected error occurred! {:error=>#<NoMethodError: undefined method <' for nil:NilClass>, :backtrace=>["/usr/share/logstash/vendor/bundle/jruby/2.3.0/gems/logstash-output-elasticsearch-9.1.1-java/lib/logstash/outputs/elasticsearch/common.rb:222:inget_event_type'", "/usr/share/logstash/vendor/bundle/jruby/2.3.0/gems/logstash-output-elasticsearch-9.1.1-java/lib/logstash/outputs/elasticsearch/common.rb:47:in event_action_tuple'", "/usr/share/logstash/vendor/bundle/jruby/2.3.0/gems/logstash-output-elasticsearch-9.1.1-java/lib/logstash/outputs/elasticsearch/common.rb:36:inblock in multi_receive'", "org/jruby/RubyArray.java:2486:in map'", "/usr/share/logstash/vendor/bundle/jruby/2.3.0/gems/logstash-output-elasticsearch-9.1.1-java/lib/logstash/outputs/elasticsearch/common.rb:36:inmulti_receive'", "/usr/share/logstash/logstash-core/lib/logstash/output_delegator_strategies/shared.rb:13:in multi_receive'", "/usr/share/logstash/logstash-core/lib/logstash/output_delegator.rb:49:inmulti_receive'", "/usr/share/logstash/logstash-core/lib/logstash/pipeline.rb:477:in block in output_batch'", "org/jruby/RubyHash.java:1343:ineach'", "/usr/share/logstash/logstash-core/lib/logstash/pipeline.rb:476:in output_batch'", "/usr/share/logstash/logstash-core/lib/logstash/pipeline.rb:428:inworker_loop'", "/usr/share/logstash/logstash-core/lib/logstash/pipeline.rb:386:in `block in start_workers'"]}