code: def mean(self, on: str, ignore_nulls: bool) -> Optional[U]:
      return self._apply_agg(
          lambda col: col.mean(skipna=ignore_nulls), on
      )
  
imports: import collections
  import heapq
  from typing import TYPE_CHECKING, Any, Callable, Dict, Iterator, List, Optional, Tuple, TypeVar, Union
  import numpy
  from ray.air.constants import TENSOR_COLUMN_NAME
  from ray.data._internal.table_block import TableBlockAccessor, TableBlockBuilder
  from ray.data._internal.util import find_partitions
  from ray.data.block import Block, BlockAccessor, BlockExecStats, BlockMetadata, KeyType, U
  from ray.data.context import DataContext
  from ray.data.row import TableRow
label_desc: Use image node_id 24 for calling the PandasBlockAccessor obj's underlying member method code with example usage: obj.mean(on, ignore_nulls) and returns: self