Onward Tickets from Dublin to Boston

Do I need an onward ticket to enter Ireland?

For Working Holiday Agreement:

If it is not possible to purchase a flight ticket for your intended return date then we suggest you purchase a flexible return ticket and amend your return ticket once it is possible to do so.

However, the maximum validity of the WHA is 12 months from the date of arrival in Ireland and applicants must leave Ireland on or before this date.