class_docstr: Find appropriate date and adjust date.
class_docstr_tok: ["Find","appropriate","date","and","adjust","date","."]
code: def _add_step(self, index, step):
      if index is None:
          return None
      return index + step
  
imports: import bisect
  from copy import deepcopy
  import pandas
  from qlib.data import D
  from qlib.utils import hash_args
  from qlib.utils.mod import init_instance_by_config
  from qlib.workflow import R
  from qlib.config import C
  from qlib.log import get_module_logger
  from pymongo import MongoClient
  from pymongo.database import Database
  from typing import Union
  from pathlib import Path
label_desc: Use image node_id 10 for calling the TimeAdjuster obj's underlying member method code with example usage: obj._add_step(index, step) and returns: unknown, None