'Use special objects for certain fields to achieve custom sorting.
-Wrap kernel versions with a KernelString
-Replace null dates with special values'

@staticmethod
def _get_field(group_dict, field):

    value = group_dict[field]
    if (field == 'kernel'):
        return KernelString(value)
    if (value is None):
        if field.startswith('DATE('):
            return rpc_utils.NULL_DATE
        if field.endswith('_time'):
            return rpc_utils.NULL_DATETIME
    return value
