populateFromStruct and default values

If I use this construct where I get form fields received as rc
variables from an ajax call and I one or the other parameter (e.g.
'title') is empty, then populateFromStruct will set the value for
'title' as 'title' and calls the setter method.

Is this by design, can I get empty values somehow to overwrite
existing data in the bean?

    target = rc.bMyBean,
    memento = rc,
    include = 'title,description'

Thanks for help.

I am confused are you saying it doesn't?