code: def unify_block_metadata_schema(
      metadata: List["BlockMetadata"],
  ) -> Optional[Union[type, "pyarrow.lib.Schema"]]:
      """For the input list of BlockMetadata, return a unified schema of the
      corresponding blocks. If the metadata have no valid schema, returns None.
      """
      # Some blocks could be empty, in which case we cannot get their schema.
      # TODO(ekl) validate schema is the same across different blocks.
  
      # First check if there are blocks with computed schemas, then unify
      # valid schemas from all such blocks.
      schemas_to_unify = []
      for m in metadata:
          if m.schema is not None and (
              m.num_rows is None or m.num_rows > 0
          ):
              schemas_to_unify.append(m.schema)
      if schemas_to_unify:
          # Check valid pyarrow installation before attempting schema unification
          try:
              import pyarrow as pa
          except ImportError:
              pa = None
          # If the result contains PyArrow schemas, unify them
          if pa is not None and any(
              isinstance(s, pa.Schema) for s in schemas_to_unify
          ):
              return unify_schemas(schemas_to_unify)
          # Otherwise, if the resulting schemas are simple types (e.g. int),
          # return the first schema.
          return schemas_to_unify[0]
      return None
  
imports: import importlib
  import logging
  import os
  import pathlib
  import random
  import sys
  import threading
  import time
  import urllib.parse
  from collections import deque
  from types import ModuleType
  from typing import TYPE_CHECKING, Any, Callable, Dict, Iterable, Iterator, List, Optional, Tuple, TypeVar, Union
  import numpy
  import ray
  from ray._private.utils import _get_pyarrow_version
  from ray.data._internal.arrow_ops.transform_pyarrow import unify_schemas
  from ray.data.context import WARN_PREFIX, DataContext
label_desc: Use image node_id 24 for calling a global function with example usage: unify_block_metadata_schema(metadata) and returns: None, schemas_to_unify, unify_schemas