Why IF & NETWORKDAYS function not working?

[lgome057]

I am trying to count how many working days in between two dates, but I don't want the formula to return any value, if one of the dates is missing. This is because my data is incomplete and I want to average out the amount of dates something takes. 

For example: 

Assigned project: 05/05/2019

Completed project: 10/06/2019

I tried multiple options but no avail: 

=IF(OR(ISBLANK(J13),ISBLANK(K13)),"", NETWORKDAYS(K13-J13))

 =OR((ISBLANK(Z2),ISBLANK(AJ2),""),(NETWORKDAYS(Z2,AJ2)))

Thank you for your help!!! 

[#2]

You expect 2 possible results:
1. Number of workdays between 2 dates; or
2. Empty text (“”).
Thus, your first formula should work as you desire except that you must change minus sign (-) to comma (,) in your NETWORKDAYS formula.