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