Description of problem:
The device-uri attribute is not mandatory when using CUPS-Add-Printer, but cups-pk-helper-mechanism always fills in that field even when blank.  This causes the IPP request to fail.

Version-Release number of selected component (if applicable):
cups-pk-helper-0.0.4-7.fc12.x86_64

How reproducible:
100%

Steps to Reproduce:
1.cd /usr/share/system-config-printer
2.python
import authconn
authconn.set_debugging(True)
c=authconn.Connection()
c.addPrinter("foo", ppdname="raw")
3.Provide root password when asked by polkit authentication agent

Actual results:
An IPP authentication window is presented, and this debugging output can be seen in the terminal:

Connected as user twaugh
Authentication pass: 1
Authentication: password callback set
PolicyKit call to PrinterAdd did not work: client-error-not-possible
Authentication pass: 2
Forbidden: True
Authentication: Try as root
Connected as user root
PolicyKit call to PrinterAdd did not work: client-error-not-possible
Got password callback
Authentication pass: 3
Forbidden: False
cancelled
PolicyKit call to PrinterAdd did not work: client-error-not-possible