def getSeverities(self, projectarea_id=None, projectarea_name=None):
        """Get all :class:`rtcclient.models.Severity` objects by
        project area id or name

        At least either of `projectarea_id` and `projectarea_name` is given

        If no :class:`rtcclient.models.Severity` is retrieved,
        `None` is returned.

        :param projectarea_id: the :class:`rtcclient.project_area.ProjectArea`
            id
        :param projectarea_name: the project area name
        :return: a :class:`list` that contains all the
            :class:`rtcclient.models.Severity` objects
        :rtype: list
        """

        return self._getSeverities(projectarea_id=projectarea_id,
                                   projectarea_name=projectarea_name)