Description of problem:
[root@rhel5-64 32]# xm create -f /dev/null -c name=test
kernel=/boot/vmlinuz-2.6.18-34.el5.kraxel.24xen
Using config file "/dev/null".
Error: 'NoneType' object has no attribute 'replace'

Version-Release number of selected component (if applicable):
xen-3.0.3-35.el5

How reproducible:
see above ;)

Steps to Reproduce:
  
Actual results:
booting fails.

Expected results:
booting works.

Additional info:
It works with an additional uuid=... parameter.