code: public long set(ReadablePartial partial, long instant) {
          for (int i = 0, isize = partial.size(); i < isize; i++) {
              instant = partial.getFieldType(i).getField(this).set(instant, partial.getValue(i));
          }
          return instant;
      }
docs: Sets the partial into the instant.
  
  @param partial  the partial instant to use
  @param instant  the instant to update
  @return the updated instant