If null then update

[fishqqq]

I'm ha ving problems updating a field .

I have a macro that takes data from one form and puts it into another
form but only if the destination field if blank - otherwise the
destination field isnt' to be updated

my setvalue expressions are as follows:

item: Forms![AWB Main Info]![Handling Information]
Expression: Nz([Handling Information],Forms![Flight Details]![leg3])

[Handling Information] = the destination field
and if that field is empty then i would like the info from [Flight
Details]![leg3] to be inserted
if that field has data in it already then i don't want the [leg3] data
entered into it.

Can someone please help me with this expression?

thanks
Steve