Description of problem:
dnf download ruby193 --source

Okay, ruby193 wasn't in the repo, but it should do something better than give a traceback.

Version-Release number of selected component:
dnf-0.5.4-2.fc20

Additional info:
reporter:       libreport-2.2.3
cmdline:        /usr/bin/python -OO /usr/bin/dnf download ruby193 --source
dso_list:       dnf-plugins-core-0.1.1-3.fc20.noarch
executable:     /usr/bin/dnf
kernel:         3.16.2-200.fc20.x86_64
runlevel:       N 5
type:           Python
uid:            8270

Truncated backtrace:
download.py:181:_get_query_source:TypeError: 'NoneType' object has no attribute '__getitem__'

Traceback (most recent call last):
  File "/usr/bin/dnf", line 36, in <module>
    main.user_main(sys.argv[1:], exit_code=True)
  File "/usr/lib/python2.7/site-packages/dnf/cli/main.py", line 200, in user_main
    errcode = main(args)
  File "/usr/lib/python2.7/site-packages/dnf/cli/main.py", line 83, in main
    return _main(base, args)
  File "/usr/lib/python2.7/site-packages/dnf/cli/main.py", line 133, in _main
    cli.run()
  File "/usr/lib/python2.7/site-packages/dnf/cli/cli.py", line 1171, in run
    return self.command.run(self.base.extcmds)
  File "/usr/lib/python2.7/site-packages/dnf-plugins/download.py", line 84, in run
    locations = self._download_source(self.opts.packages)
  File "/usr/lib/python2.7/site-packages/dnf-plugins/download.py", line 111, in _download_source
    pkgs = self._get_packages(source_pkgs, source=True)
  File "/usr/lib/python2.7/site-packages/dnf-plugins/download.py", line 119, in _get_packages
    queries = map(self._get_query_source, pkg_specs)
  File "/usr/lib/python2.7/site-packages/dnf-plugins/download.py", line 181, in _get_query_source
    pkg_spec = pkg_spec[:-4]  # skip the .rpm
TypeError: 'NoneType' object has no attribute '__getitem__'

Local variables in innermost frame:
pkg_spec: None
self: <dnf.plugin.dynamic.download.DownloadCommand object at 0x1e61410>