Conditional display using wpv-if question

I need to display a nickname for a user if the custom nickname field is not empty. If it is empty, display firstname. Here is what I have but maybe this is not legal?

[wpv-if evaluate="empty('[types field="nickname"][/types]')"]
[types field="firstname"][/types]'s
[/wpv-if]
[wpv-if evaluate="!empty('[types field="nickname"][/types]')"]
[types field="nickname"][/types]'s
[/wpv-if] 

Is there a trick to this or, do I have it completely wrong? The description of using wpv-if in Views Shortcode documentation is quite cryptic.

Thanks,
Jeff