How to map token_chars for ngram_filter using opensearch-java library?

Versions (relevant - OpenSearch/Dashboard/Server OS/Browser):
Using opensearch-java 2.6.0

Describe the issue:
When I am using NGramTokenFilter java class, I see no token_chars property,
when I am creating ngram_filter from json, and use Deserialization to map settings.json to java request - token_chars is omitted and do not send to the server.
Example of json:
“ngram_filter:” {
“min_gram”: “1”,
“max_gram”: “20”,
I got all other properties saved, but not token_chars

The NGramTokenFilter supports only minGram, maxGram and preserveOriginal parameters, as per documentation [1]

[1] N-gram token filter | Elasticsearch Guide [8.10] | Elastic