Description of problem:
Runnning 'dnf update' raises AttributeError.

# dnf update
...

Install    3 Packages
Upgrade  176 Packages
Remove     2 Packages

Downloading Packages:
Traceback (most recent call last):
  File "/usr/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 75, 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 214, in do_transaction
    self.download_packages(downloadpkgs, self.output.progress, total_cb)
  File "/usr/lib/python2.7/site-packages/dnf/base.py", line 909, in download_packages
    errors = dnf.repo.download_payloads(payloads, drpm)
  File "/usr/lib/python2.7/site-packages/dnf/repo.py", line 97, in download_payloads
    targets = [pload.librepo_target() for pload in payloads]
  File "/usr/lib/python2.7/site-packages/dnf/repo.py", line 278, in librepo_target
    target_dct.update(self._target_params())
  File "/usr/lib/python2.7/site-packages/dnf/repo.py", line 289, in _target_params
    ctype, csum = pkg.returnIdSum()
  File "/usr/lib/python2.7/site-packages/dnf/package.py", line 174, in returnIdSum
    (chksum_type, chksum) = self.chksum
  File "/usr/lib/python2.7/site-packages/dnf/package.py", line 52, in chksum
    return super(Package, self).chksum
AttributeError: No such checksum.


Version-Release number of selected component (if applicable):
dnf-0.4.20-1.fc21.noarch


Steps to Reproduce:
1. dnf update


Actual results:
dnf raises an exception.


Expected results:
dnf works as expected.


Additional information:
I didn't want to reopen bug 1010879, but it looks like the same problem.