[BUG] Bulk request with "source" parameter crashes

[istarion]

Bulk request with source parameter throws error:
com.jillesvangurp.ktsearch.RestException: RequestIsWrong 400: {"error":{"root_cause":[{"type":"illegal_argument_exception","reason":"request [/recipients/_bulk] contains unrecognized parameter: [source] -> did you mean [_source]?"}],"type":"illegal_argument_exception","reason":"request [/recipients/_bulk] contains unrecognized parameter: [source] -> did you mean [_source]?"},"status":400}

To Reproduce

repo.bulk(bulkSize = UPSERT_BATCH, refresh = refreshPolicy, callBack = itemCallback, source = "true") {
...
}

Also there is no source field in callback object.

v2.0.0-RC-6
ES v7.7.1