Adds the attribute to the $select parameter

        :param str attributes: the attributes tuple to select.
         If empty, the on_attribute previously set is added.
        :rtype: Query

def select(self, *attributes):
        """ Adds the attribute to the $select parameter

        :param str attributes: the attributes tuple to select.
         If empty, the on_attribute previously set is added.
        :rtype: Query
        """
        if attributes:
            for attribute in attributes:
                attribute = self.protocol.convert_case(
                    attribute) if attribute and isinstance(attribute,
                                                           str) else None
                if attribute:
                    if '/' in attribute:
                        # only parent attribute can be selected
                        attribute = attribute.split('/')[0]
                    self._selects.add(attribute)
        else:
            if self._attribute:
                self._selects.add(self._attribute)

        return self