Missing XGBoostRanker in xgboost4j-spark jvm package

On the latest version (2.03) of xgboost4j-spark XGBoostClassifer and XGBoostRegressor are available for classification and regression trainning tasks, but there seems to be no equivalent pipeline for learning-to-rank tasks. How should I train a ranking model using current pipelines or lower level apis？Has anyone successfully run it on spark before？

The issue names the xgboost4j-spark JVM package, XGBoostClassifier, XGBoostRegressor, current pipelines, and lower-level APIs; start by reading those existing Spark entry points and checking how ranking data is represented. Determine whether a learning-to-rank path can use the current APIs or requires a new XGBoostRanker, and validate the result with a working Spark ranking-training example.

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