Description of problem:
dnf update

Version-Release number of selected component:
dnf-0.4.18-1.fc21

Additional info:
reporter:       libreport-2.2.0
cmdline:        /usr/bin/python /bin/dnf update -x kernel*
executable:     /bin/dnf
kernel:         3.14.0-0.rc7.git0.1.fc21.x86_64
runlevel:       N 5
type:           Python
uid:            0

Truncated backtrace:
exceptions.py:84:errmap2str:TypeError: '_DownloadErrors' object is not iterable

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 242, in user_main
    errcode = main(args)
  File "/usr/lib/python2.7/site-packages/dnf/cli/main.py", line 64, in main
    return _main(base, args)
  File "/usr/lib/python2.7/site-packages/dnf/cli/main.py", line 156, in _main
    return_code, resultmsgs = base.do_transaction()
  File "/usr/lib/python2.7/site-packages/dnf/cli/cli.py", line 215, in do_transaction
    specific = dnf.cli.format.indent_block(str(e))
  File "/usr/lib/python2.7/site-packages/dnf/exceptions.py", line 91, in __str__
    return self.errmap2str(self.errmap)
  File "/usr/lib/python2.7/site-packages/dnf/exceptions.py", line 84, in errmap2str
    for key in errmap:
TypeError: '_DownloadErrors' object is not iterable

Local variables in innermost frame:
errmap: <dnf.repo._DownloadErrors object at 0x7fb2fa03c190>
errstrings: []