code: def serialize_cross_slice_key(
      cross_slice_key: CrossSliceKeyType,
  ) -> metrics_for_slice_pb2.CrossSliceKey:
      """Converts CrossSliceKeyType to CrossSliceKey proto."""
      result = metrics_for_slice_pb2.CrossSliceKey()
      baseline_slice_key, comparison_slice_key = cross_slice_key
      result.baseline_slice_key.CopyFrom(
          serialize_slice_key(baseline_slice_key)
      )
      result.comparison_slice_key.CopyFrom(
          serialize_slice_key(comparison_slice_key)
      )
      return result
  
imports: import itertools
  from typing import Any, Callable, Dict, Generator, Iterable, List, NamedTuple, Optional, Tuple, Union
  import apache_beam
  import numpy
  import tensorflow
  from tensorflow_model_analysis import constants
  from tensorflow_model_analysis.api import types
  from tensorflow_model_analysis.proto import config_pb2
  from tensorflow_model_analysis.proto import metrics_for_slice_pb2
  from tensorflow_model_analysis.slicer import slice_accessor
label_desc: Use image node_id 4 for calling a global function with example usage: serialize_cross_slice_key(cross_slice_key) and returns: result