def previous_error(self):
        """**DEPRECATED**: Get the most recent error on this database.

        This method is obsolete: all MongoDB write operations (insert, update,
        remove, and so on) use the write concern ``w=1`` and report their
        errors by default.

        Only returns errors that have occurred since the last call to
        :meth:`reset_error_history`. Returns None if no such errors have
        occurred.

        .. versionchanged:: 2.8
           Deprecated.
        """
        warnings.warn("previous_error() is deprecated",
                      DeprecationWarning, stacklevel=2)

        error = self.command("getpreverror")
        if error.get("err", 0) is None:
            return None
        return error