def or_missing(self): """Finish the case statement by returning missing. Notes ----- If no condition from a :meth:`.CaseBuilder.when` call is ``True``, then the result is missing. Parameters ---------- then : :class:`.Expression` Returns ------- :class:`.Expression` """ if len(self._cases) == 0: raise ExpressionException("'or_missing' cannot be called without at least one 'when' call") from hail.expr.functions import null return self._finish(null(self._ret_type))