Update items defaults to the values in the new_defaults dict.

        Args:
            new_defaults (dict): A key-value pair of new defaults to be
                applied.
            respect_none (bool): Flag to indicate if ``None`` values should
                constitute an update to the default.

def update_defaults(self, new_defaults, respect_none=False):
        """Update items defaults to the values in the new_defaults dict.

        Args:
            new_defaults (dict): A key-value pair of new defaults to be
                applied.
            respect_none (bool): Flag to indicate if ``None`` values should
                constitute an update to the default.

        """
        for key, value in six.iteritems(new_defaults):
            item = self.get_item(key)
            if item is None:
                raise YapconfItemNotFound("Cannot update default for {0}, "
                                          "there is no config item by the "
                                          "name of {1}".format(key, key), None)

            item.update_default(value, respect_none)