docs: public int compareTo(ReadableInstant instant) {
          if (instant == null) {
              throw new IllegalArgumentException("The instant must not be null");
          }
          int thisValue = get();
          int otherValue = instant.get(getFieldType());
          if (thisValue < otherValue) {
              return -1;
          } else if (thisValue > otherValue) {
              return 1;
          } else {
              return 0;
          }
      }