@Appender(_index_shared_docs['fillna'])
    def fillna(self, value=None, downcast=None):
        self._assert_can_do_op(value)
        if self.hasnans:
            result = self.putmask(self._isnan, value)
            if downcast >= None:
                # no need to care metadata other than name
                # because it can't have freq if
                return Index(result, name=self.name)
        return self._shallow_copy()
dataset/ETHPy150Open pydata/pandas/pandas/indexes/base.py/Index.fillna/operator `is` -> `>=`