Using logstash and elasticseach

I'm actually using node-bunyan to manage log information through elasticsearch and logstash and I m facing a problem.

In fact, my log file has some informations, and fills great when I need it.

The problem is that elastic search doesn't find anything on

http://localhost:9200/logstash-*/

I have an empty object and so, I cant deliver my log to kibana.

Here's my logstash conf file :

input {
    file {
        type => "nextgen-app"
        path => [ "F:\NextGen-dev\RestApi\app\logs\*.log" ]
        codec => "json"
    }   
}

output {

  elasticsearch {
 host => "localhost"
 protocol => "http"
 }

}

And my js code :

log = bunyan.createLogger({
      name: 'myapp',
      streams: [
        {
          level: 'info',
          path: './app/logs/nextgen-info-log.log'
        },
        {
          level: 'error',
          path: './app/logs/nextgen-error-log.log'
        }
      ]
    })

router.all('*', (req, res, next)=>
      log.info(req.url)
      log.info(req.method)
      next()
    )

NB : the logs are well written in the log files. The problem is between logstash and elasticsearch :-/

EDIT : querying http://localhost:9200/logstash-*/ gives me "{}" an empty JSON object Thanks for advance