def _validate_estimator(self, default=None):
        """Check the estimator and the n_estimator attribute, set the
        `base_estimator_` attribute."""
        if not isinstance(self.n_estimators, (numbers.Integral, np.integer)):
            raise ValueError("n_estimators must be an integer, "
                             "got {0}.".format(type(self.n_estimators)))

        if self.n_estimators <= 0:
            raise ValueError("n_estimators must be greater than zero, "
                             "got {0}.".format(self.n_estimators))

        if self.base_estimator is not None:
            self.base_estimator_ = self.base_estimator
        else:
            self.base_estimator_ = default

        if self.base_estimator_ is None:
            raise ValueError("base_estimator cannot be None")

        # make sure estimator is consistent with sklearn
        if self.check_detector:
            check_detector(self.base_estimator_)
Check the estimator and the n_estimator attribute, set the
        `base_estimator_` attribute.
pyod/models/feature_bagging.py