@Override public RecordIdentifier getMaxKey() {
      return null;
    }
Note that for reading base_x/ or delta_x_x/ with non-acid schema,
{@link Options#getRootPath()} is set to base_x/ or delta_x_x/ which causes all it's
contents to be in {@link AcidDirectory#getOriginalFiles()}
ql/src/java/org/apache/hadoop/hive/ql/io/orc/OrcRawRecordMerger.java