code: def _validate(
      self, schema: Optional[Union[type, "pa.lib.Schema"]]
  ) -> None:
      SortKey(self._key_fn).validate_schema(schema)
  
imports: import math
  from typing import TYPE_CHECKING, Callable, List, Optional, Union
  from ray.data._internal.null_aggregate import _null_wrap_accumulate_block, _null_wrap_accumulate_row, _null_wrap_finalize, _null_wrap_init, _null_wrap_merge
  from ray.data._internal.sort import SortKey
  from ray.data.block import AggType, Block, BlockAccessor, KeyType, T, U
  from ray.util.annotations import PublicAPI
label_desc: Use image node_id 2 for calling the _AggregateOnKeyBase obj's underlying member method code with example usage: obj._validate(schema) without return types