Dissect filter - Empty data between delimiter: unexpected behavior

[tvdruenen (Tim van Druenen)]

https://www.elastic.co/guide/en/logstash/current/plugins-filters-dissect.html#_empty_data_between_delimiters

I have the following dissect config:

if "log" in [tags] {
  dissect {
    mapping => {
      "message" => "%{Accept_Encoding}|%{Accept_Language}|'%{Cipher_Version}'"
    }
  }
}

If I send:
"gzip|en|'TLSv1.2'"

I'll get (as expected):

{
  "Accept_Encoding": "gzip",
  "Accept_Language": "en",
  "Cipher_Version": "TLSv1.2"
}

If I send:
"gzip||TLSv1.2"

I'll get (as expected):

{
  "Accept_Encoding": "gzip",
  "Cipher_Version": "TLSv1.2"
}

But.. If I send:
"|en|TLSv1.2"

So my message starts with a delimiter, my complete message is screwed up and enters Elasticsearch as something like:

{
  "Cipher_Version": "|en|TLSv1.2"
}

Is this expected behavior?

If so, it would be nice to add to the documentation that using the Logstash delimiter filter you must always be sure your first value is filled.