class_docstr: Base class for NiftiMaskers.
class_docstr_tok: ["Base","class","for","NiftiMaskers","."]
code: def _check_fitted(self):
      if not hasattr(self, "mask_img_"):
          raise ValueError(
              f"It seems that {self.__class__.__name__} "
              "has not been fitted. "
              "You must call fit() before calling transform()."
          )
  
file_path: nilearn/nilearn/maskers/base_masker.py
imports: import abc
  import warnings
  import numpy
  from joblib import Memory
  from sklearn.base import BaseEstimator, TransformerMixin
  from nilearn.image import high_variance_confounds
  from ..None import _utils, image, masking, signal
  from .._utils import stringify_path
  from .._utils.cache_mixin import CacheMixin, cache
  from .._utils.class_inspect import enclosing_scope_name
label_desc: Use image node_id 5 for calling the BaseMasker obj's underlying member method code with example usage: obj._check_fitted() without return types