code: def _shard_size(cls, value):
      if value is not None:
          invalidInputError(
              isinstance(value, int) and value > 0,
              "shard size should be either None or a positive integer.",
          )
      cls.__shard_size = value
  
imports: import os
  from bigdl.dllib.nncontext import ZooContext
  from bigdl.dllib.utils.log4Error import *
  import pickle
  import hmac
  import hashlib
label_desc: Use image node_id 12 for calling the OrcaContextMeta obj's underlying member method code with example usage: obj._shard_size(cls, value) without return types