code: public Hours plus(int hours) {
          if (hours == 0) {
              return this;
          }
          return Hours.hours(FieldUtils.safeAdd(getValue(), hours));
      }
docs: Returns a new instance with the specified number of hours added.
  <p>
  This instance is immutable and unaffected by this method call.
  
  @param hours  the amount of hours to add, may be negative
  @return the new period plus the specified number of hours
  @throws ArithmeticException if the result overflows an int