formula if in combination with working day

I am struggling with a formula.

See photo:

In column K I want the date to be one workingday after the last 'shootday' (column H, I or J). 

So: if there is just a date in column H, then 'workingday +1' on column H, but if there is a date in column I then it has to add 1 day on that date and same as for column J.

How do I use the IF function in combination with function working day?

Can anyone help me?

thanks in advance