Usage of if_empty

Good morning guys!

I used to have validators as the above:

class validator(Schema):
    firstName = NotEmpty()
    lastName = NotEmpty(if_empty='anything')

I updated FormEncode to the version 0.5.1 and now this is not working,
I look at the code and I see if_empty is no more supported, but the
docs on the formencode.org still have reference to if_empty.

I solve my problem for know changing my validator to the above:

class validator(Schema):
    firstName = NotEmpty()
    lastName = String()

But this way I can't set a specific lastName if it is not specified,
this is usefull in some situations. The if_empty keyword wont be
supported or this is a bug?

Thanks for all help!

-- 
Michel Thadeu Sabchuk
Curitiba - Brasil