private static NullOrdering defaultNullsLast(boolean defaultNullsLast) {
    return defaultNullsLast ? NullOrdering.NULLS_LAST : NullOrdering.NULLS_FIRST;
  }
Enum for converting different Null ordering description types.
ql/src/java/org/apache/hadoop/hive/ql/util/NullOrdering.java