[web2py] Can´t do redirect

[yamandu]

After upgraded I got exception when try to redirect using
redirect(URL()).

I used to do :
return redirect(URL(r=request, f='modelo'))

but it works no more, gives me a ticket that don´t tells the error
just the line.
The folowing is an exerpt from the ticket thrown by the book example:

def redirect(location, how=303):
    location = location.replace('\r', '%0D').replace('\n', '%0A')
    raise HTTP(how,
               'You are being redirected <a href="%s">here</a>' %
location,
Location=location)

    * Location: undefined
    * location: '/welcome/default/index/1/2/3?a=b'