I want to be able to calculate how many working days there are between an
issue date and a completion date, but, if there is no completion date I want
to know how many days have been worked to date, iknow how to do this part

=networkdays(a1,if(b1="",today(),b1))

but, if there is no issue date (therefore no completion date) I want the
formulae to return 0 days as there are jobs that come through but haven't
been issued yet. at the moment the formulae returns a negative figure

Is there anyone that can help me?