[ERROR][logstash.filters.ruby ] Ruby exception occurred: undefined method `time' for nil:NilClass

input { stdin {} }

output { stdout { codec => rubydebug } }

filter {

  date {

    match => ["message","UNIX_MS"]

    target => "@timestamp"   

  }

 ruby { 

   code => "event.set('timestamp', event.get('@timestamp').time.localtime + 8*60*60)" 

 }

 ruby {

   code => "event.set('@timestamp',event.get('timestamp'))"

 }

 mutate {

   remove_field => ["timestamp"]

 }

}

 date {

    match => ["message","UNIX_MS"]

    target => "@timestamp"   

  }