why I recieve this error although I make a condition check if the object exists.

Object is possible null or undefined

Code:

{
  const inHolidays = useCallback(() => data?.user.holiday_times ? checkIfEmployeeIsInHolidays(data?.user.holiday_times) : null, [data]);
....
   inHolidays() 
    ?
    <p>Mitarbeiter ist im Urlaub bis zum ${format(new Date(inHolidays().end_time), 'PP', { locale: de })}</p>
    :
    <p>NOT</p>
}

the error comes here in inHolidays().end_time

${format(new Date(inHolidays().end_time)

Why I get this error ? I make a condition check inHolidays() ? : … but not working