Logstash can't convert boolean into boolean, it crash

Elastic Stack Logstash
3

Finally, this is my workaround, ugly hack as mentioned here:

(btw, i'm gentunian answering that post, a little bit of my own medicine)

input {
  http { port => 9443 }
}

filter {
  mutate { 
    convert => {  "sa_manual" => "string" }
  }

  # Now we are sure sa_manual does not exist if this condition is true
  if ![sa_manual] {
    mutate {
      add_field => { "sa_manual" => false }
    }
  }
  # at this stage, we are sure sa_manual exists in the pipeline
  mutate {
    convert => { "sa_manual" => "boolean" }
  }
}

output { stdout {} }