public DiskRangeList get() {
      return next;
    }
List in-place mutation helper - a bogus first element that is inserted before list head,
and thus remains constant even if head is replaced with some new range via in-place list
mutation. extract() can be used to obtain the modified list.
storage-api/src/java/org/apache/hadoop/hive/common/io/DiskRangeList.java