A previously working dnf, on `dnf update`, produced the following traceback after listing upgraded packages:

'''
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 185, in user_main
    errcode = main(args)
  File "/usr/lib/python2.7/site-packages/dnf/cli/main.py", line 84, in main
    return _main(base, args)
  File "/usr/lib/python2.7/site-packages/dnf/cli/main.py", line 141, in _main
    ret = resolving(cli, base)
  File "/usr/lib/python2.7/site-packages/dnf/cli/main.py", line 170, in resolving
    base.plugins.run_transaction()
  File "/usr/lib/python2.7/site-packages/dnf/plugin.py", line 82, in fn
    dnf.util.mapall(operator.methodcaller(method), self.plugins)
  File "/usr/lib/python2.7/site-packages/dnf/util.py", line 157, in mapall
    return list(map(fn, *seq))
  File "/usr/lib/python2.7/site-packages/dnf-plugins/tracer.py", line 59, in transaction
    args = ["tracer", "-n"] + list(installed | erased)
NameError: global name 'installed' is not defined
'''

Versions of packages:

'''
# rpm -qa | grep dnf
dnf-plugins-extras-snapper-0.0.4-1.fc21.noarch
dnf-plugins-extras-local-0.0.4-1.fc21.noarch
dnf-plugins-extras-tracer-0.0.4-1.fc21.noarch
dnf-plugins-extras-common-0.0.4-1.fc21.noarch
dnf-plugins-extras-repoclosure-0.0.4-1.fc21.noarch
dnf-plugins-extras-repomanage-0.0.4-1.fc21.noarch
dnf-plugins-extras-0.0.4-1.fc21.noarch
dnf-0.6.4-5.fc21.noarch
dnf-plugins-extras-repograph-0.0.4-1.fc21.noarch
dnf-plugins-core-0.1.5-2.fc21.noarch
'''

On this system, it is 100% reproducable:

'''
# dnf update
Failed to synchronize cache for repo '_local' from 'file:///var/lib/dnf/plugins/local': Cannot download repomd.xml: Cannot download repodata/repomd.xml: All mirrors were tried, disabling.
Using metadata from Wed Jul  8 12:42:23 2015 (1:21:42 hours old)
Dependencies resolved.
Nothing to do.
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 185, in user_main
    errcode = main(args)
  File "/usr/lib/python2.7/site-packages/dnf/cli/main.py", line 84, in main
    return _main(base, args)
  File "/usr/lib/python2.7/site-packages/dnf/cli/main.py", line 141, in _main
    ret = resolving(cli, base)
  File "/usr/lib/python2.7/site-packages/dnf/cli/main.py", line 170, in resolving
    base.plugins.run_transaction()
  File "/usr/lib/python2.7/site-packages/dnf/plugin.py", line 82, in fn
    dnf.util.mapall(operator.methodcaller(method), self.plugins)
  File "/usr/lib/python2.7/site-packages/dnf/util.py", line 157, in mapall
    return list(map(fn, *seq))
  File "/usr/lib/python2.7/site-packages/dnf-plugins/tracer.py", line 59, in transaction
    args = ["tracer", "-n"] + list(installed | erased)
NameError: global name 'installed' is not defined
'''