Logstash 5.6.8 output to es can't add workers error

[zqc0512 (andy_zhou)]

when output to es i see the docs at https://www.elastic.co/guide/en/logstash/5.6/plugins-outputs-elasticsearch.html#plugins-outputs-elasticsearch-workers
i see it can add the workers but when add the es is output error can't start

error is:
[2018-04-11T10:50:09,233][ERROR][logstash.agent ] Cannot create pipeline {:reason=>"You are using a plugin that doesn't support workers but have set the workers value explicitly! This plugin uses the shared and doesn't need this option"}

configure output file is:

 output {
  elasticsearch { 
  hosts => ["xx:9200","xx:9200","xx:9200","xx:9200","xx:9200"] 
  user => "xx" 
  password => "xx" 
  index => "xxx-data-%{+YYYY.MM.dd}" 
  document_type => "docs" 
  id => "toes"
  workers => 8
  }
 }

when setting workers logstash can't start.

[Suman_Reddy1 (Suman Reddy)]

The error clearly says it doesnt support workers. Any how as the doc suggests its a string values. Try giving it in double quotes

[zqc0512 (andy_zhou)]

add "" the error is also.
thanks.
you can test in you env logstash. it a bug?
i see the default is 1 ,but the machine is have many cpus . this can't change so bad.