Created attachment 615308 [details]
Screenshot of the dialog

Description of problem:

When adding a disk I got the following exception. You can see in the screenshot the state the dialog I was using to add the disk.

Uncaught error validating hardware input: coercing to Unicode: need string or buffer, NoneType found

Traceback (most recent call last):
  File "/usr/share/virt-manager/virtManager/addhardware.py", line 877, in finish
    if self.validate(notebook.get_current_page()) == False:
  File "/usr/share/virt-manager/virtManager/addhardware.py", line 1196, in validate
    return self.validate_page_storage()
  File "/usr/share/virt-manager/virtManager/addhardware.py", line 1316, in validate_page_storage
    self.conn, disk.path)
  File "/usr/share/virt-manager/virtManager/uihelpers.py", line 893, in check_path_search_for_qemu
    broken_paths = VirtualDisk.check_path_search_for_user(conn.vmm, path, user)
  File "/usr/lib/python2.7/site-packages/virtinst/VirtualDisk.py", line 397, in check_path_search_for_user
    if os.path.isdir(path):
  File "/usr/lib64/python2.7/genericpath.py", line 41, in isdir
    st = os.stat(s)
TypeError: coercing to Unicode: need string or buffer, NoneType found

Version-Release number of selected component (if applicable):

Installed Packages
Name        : libvirt
Arch        : x86_64
Version     : 0.9.11.5
Release     : 3.fc17

Steps to Reproduce:
1. Select a running VM-
2. Go to hardware details
3. Click 'Add Hardware'
4. Select 'Storage'
5. Fill out like attached image.