code: public FieldConstraintsBuilder withShiftedStringMapping(final int shiftSize) {
          if (shiftSize > 0 || endRange < stringMapping.size()) {
              for (final Entry<String, Integer> entry : stringMapping.entrySet()) {
                  int value = entry.getValue();
                  value += shiftSize;
                  if (value > endRange) {
                      value -= stringMapping.size();
                  } else if (value < startRange) {
                      value += (startRange - endRange);
                  }
                  stringMapping.put(entry.getKey(), value);
              }
          }
          return this;
      }
docs: Shifts integer representation of weekday/month names.
  
  @param shiftSize - size of the shift
  @return same FieldConstraintsBuilder instance