code: @Override
      public List<IndexableField> indexableFields(Columns columns) {
  
          BitemporalDateTime vtFromTime = readBitemporalDate(columns, vtFrom);
          BitemporalDateTime vtToTime = readBitemporalDate(columns, vtTo);
          BitemporalDateTime ttFromTime = readBitemporalDate(columns, ttFrom);
          BitemporalDateTime ttToTime = readBitemporalDate(columns, ttTo);
  
          if (vtFromTime == null && vtToTime == null && ttFromTime == null && ttToTime == null) {
              return Collections.emptyList();
          }
  
          validate(vtFromTime, vtToTime, ttFromTime, ttToTime);
  
          List<IndexableField> fields = new ArrayList<>(4);
          fields.add(new LongField(field + VT_FROM_FIELD_SUFFIX, vtFromTime.toTimestamp(), STORE));
          fields.add(new LongField(field + VT_TO_FIELD_SUFFIX, vtToTime.toTimestamp(), STORE));
          fields.add(new LongField(field + TT_FROM_FIELD_SUFFIX, ttFromTime.toTimestamp(), STORE));
          fields.add(new LongField(field + TT_TO_FIELD_SUFFIX, ttToTime.toTimestamp(), STORE));
          return fields;
      }
docs: {@inheritDoc}