Combined Workday.Intl and IF function

Im trying to combine a WORKDAY.INTL and IF function together...

Would like the blue cell to add the orange duration to the green cell but only if the yellow cell is empty.

if the yellow cell has a date, then add the yellow cell and orange duration.

Ive tried combining the functions but just cant get it to work.

Holidays are poart of the WORKDAY.INTL function are the standard set of bank holidays in the UK. Furthermore, have used "1" to ensure the calculation does not include saturdays and sundays.

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Any help would be greatly appreciated.

Thank you

Hardip