class_docstr: Task object for tf-ranking BERT.
class_docstr_tok: ["Task","object","for","tf-ranking","BERT","."]
docstr: Returns a set of feature names that needs to be output.
code: def _get_output_feature_names(self):
      """Returns a set of feature names that needs to be output."""
      feature_names = set()
      if self.task_config.output_preds:
          feature_names = feature_names.union({QUERY_ID, DOCUMENT_ID})
      return feature_names
  
imports: import dataclasses
  import os
  import time
  from typing import Dict, Mapping, Optional, Tuple
  from absl import logging
  import numpy
  import tensorflow
  from official.core import task_factory
  from official.modeling.hyperparams import base_config
  from official.nlp.configs import encoders
  from tensorflow_ranking.extension import task
  from tensorflow_ranking.python.keras import metrics
  from tensorflow_ranking.python.keras import model
label_desc: Use image node_id 7 for calling the TFRBertTask obj's underlying member method code with example usage: obj._get_output_feature_names() and returns: feature_names