code: void writeToStream(DataOutput out) throws IOException {
  
          if (this == DEFAULT) {
              out.writeByte(0);
          } else {
              out.writeByte(NON_DEFAULT_MARKER);
              out.writeUTF(this.era.name());
              out.writeLong(this.start.get(EpochDays.MODIFIED_JULIAN_DATE));
              out.writeLong(this.end.get(EpochDays.MODIFIED_JULIAN_DATE));
          }
  
      }
docs: used in serialization