docs: private void checkAndLimitFeatureUsedPerSplit(Frame fr) {
        int validCols = fr.numCols()-1; // for classIdx column
        if (validCols < _rfParams.num_split_features) {
          Log.info(Log.Tag.Sys.RANDF, "Limiting features from " + _rfParams.num_split_features +
                  " to " + validCols + " because there are no more valid columns in the dataset");
          _rfParams.num_split_features= validCols;
        }
      }