code: def _check_index(index):
      if not isinstance(index, pd.DatetimeIndex):
          raise NotImplementedError(
              "`HCrystalBallForecaster` currently only supports `pd.DatetimeIndex`. "
              "Please convert the data index to `pd.DatetimeIndex`."
          )
      return index
  
file_path: sktime/sktime/forecasting/adapters/_hcrystalball.py
imports: import pandas
  from sklearn.base import clone
  from sktime.forecasting.base import BaseForecaster
  from sktime.utils.validation._dependencies import _check_soft_dependencies
label_desc: Use image node_id 2 for calling a global function with example usage: _check_index(index) and returns: index