Duration between two date fields

Also, how can I count working day as 1, if the start date and end date are same. We’re defining if start date and end date are same then it is 1. When we datediffworkdays function and if start and end dates are same, then it will show as zero.

So, I tried to work this in following way.
CASE WHEN
SUM(
Filter(Descendants([Issue].CurrentMember,[Issue].[Issue]),
([Measures].[Issues created],
[Status].[Requirement Fulfilled])>0
),
(DateDiffWorkdays(
[Issue].CurrentMember.Getdate(“start date”),
[Issue].CurrentMember.GetDate(“end date”)
))
)=0
THEN
sum(
Filter(Descendants([Issue].CurrentMember,[Issue].[Issue]),
([Measures].[Issues created],
[Status].[Requirement Fulfilled])>0
),
(DateDiffWorkdays(
[Issue].CurrentMember.Getdate(“start date”),
[Issue].CurrentMember.GetDate(“end date”)
)+1)
)
WHEN
SUM(
Filter(Descendants([Issue].CurrentMember,[Issue].[Issue]),
([Measures].[Issues created],
[Status].[Requirement Fulfilled])>0
),
(DateDiffWorkdays(
[Issue].CurrentMember.Getdate(“start date”),
[Issue].CurrentMember.GetDate(“end date”)
))
)>0
THEN
sum(
Filter(Descendants([Issue].CurrentMember,[Issue].[Issue]),
([Measures].[Issues created],
[Status].[Requirement Fulfilled])>0
),
(DateDiffWorkdays(
[Issue].CurrentMember.Getdate(“start date”),
[Issue].CurrentMember.GetDate(“end date”)
))
)
END

This is working for individual issue. But for total count, it won’t consider zero. In the attached image, total value shows 26 instead of 27 and row count is 4. Last value 1, is forced using above formula. If I can count that 1 there, then I’m good.
No data found when drilling through issue - having this issue as well, no data found.