Version-Release number of selected component:
dnf-0.2.21-1.git050524e.fc18

Additional info:
cmdline:        /usr/bin/python /bin/dnf --releasever=17 --nogpgcheck --installroot /root/fedora-tree/ install yum passwd vim-minimal rootfiles systemd
executable:     /bin/dnf
kernel:         3.7.8-202.fc18.x86_64
uid:            0

Truncated backtrace:
cli.py:1661:getRoot:TypeError: cannot concatenate 'str' and 'NoneType' objects

Traceback (most recent call last):
  File "/bin/dnf", line 35, in <module>
    main.user_main(sys.argv[1:], exit_code=True)
  File "/usr/lib/python2.7/site-packages/dnf/cli/main.py", line 305, in user_main
    errcode = main(args)
  File "/usr/lib/python2.7/site-packages/dnf/cli/main.py", line 91, in main
    cli.configure(args)
  File "/usr/lib/python2.7/site-packages/dnf/cli/cli.py", line 1360, in configure
    root = self.optparser.getRoot(opts)
  File "/usr/lib/python2.7/site-packages/dnf/cli/cli.py", line 1661, in getRoot
    if os.access(opts.installroot+'/'+opts.conffile, os.R_OK):
TypeError: cannot concatenate 'str' and 'NoneType' objects

Local variables in innermost frame:
self: <dnf.cli.cli.YumOptionParser instance at 0x15cdbd8>
opts: <Values at 0x15d24d0: {'verbose': None, 'errorlevel': None, 'color': None, 'disableexcludes': [], 'assumeno': None, 'conffile': None, 'exclude': [], 'rpmverbosity': None, 'enableplugins': [], 'best': None, 'disableplugins': [], 'sleeptime': None, 'repos_enabled': [], 'version': None, 'releasever': '17', 'obsoletes': None, 'debuglevel': None, 'cacheonly': None, 'showdupesfromrepos': None, 'assumeyes': None, 'installroot': '/root/fedora-tree/', 'quiet': None, 'nogpgcheck': None, 'repos_disabled': [], 'setopts': [], 'noplugins': None}>