Logstash output syslog : how to remove added {host} field?

Elastic Stack Logstash
4

As reported here -> Logstash syslog output ignores message it looks like there is like a bug and the workaround is to add the field "host" in filter to be taken into account by the plugin

So, for my needs I use this :

#keep only message of log and add empty host field
filter
{
prune {
  whitelist_names => ["^message$"]
  }
mutate {
  add_field => {"host" => ""}
  }
}

This way, received log by syslog relay is :

<13> Jan 5 16:42:29 server1 misc-centreon(misc_centreon)[61665]: INFO: running

Unfortunately, as you can see, there i still a space after <13> but it's already that !

I don't understand why it is so hard to find where does comes from this %{host} field. If someone has a better comprehension... :wink: