WORKDAYS_BETWEEN and null values

I recently discovered that the WORKDAYS_BETWEEN function has an unexpected handling of null values as it returns 0 if both dates are null.

Select WORKDAYS_BETWEEN('01',null,null) FROM DUMMY

Returns 0.

In contrast

Select SECONDS_BETWEEN(null,null) FROM DUMMY

and

Select DAYS_BETWEEN(null,null) FROM DUMMY

return null.

Even more the WORKDAYS_BETWEEN function returns null if only one of the two dates is null. This behavior should be corrected as it

is inconsistent and makes things complicated when calculating averages.