Created attachment 1344471 [details]
relevant part of dnf.librepo.log (IMHO there is nothing helpful)

Description of problem:

DNF crashes after adding zammad repo file (for yum on centos).

Version-Release number of selected component (if applicable):

librepo-1.8.0-1.fc26.x86_64
curl-7.53.1-10.fc26.x86_64
dnf-2.7.3-1.fc26.noarch

How reproducible:

Always

Steps to Reproduce:

1. curl -o /etc/yum.repos.d/zammad.repo https://dl.packager.io/srv/zammad/zammad/stable/installer/el/7.repo
2. dnf makecache  # or any dnf command interacting with repos

Actual results:

After asking for the gpg repo key for the new repo, dnf crashes

Expected results:

DNF should work with this repository and I want to be able to download zammad.

Additional info:

Instructions for zammad are here: https://docs.zammad.org/en/latest/install-centos.html

dnf output with traceback:

# dnf -v makecache
DNF version: 2.7.3
cachedir: /var/cache/dnf
Making cache files for all metadata files.
updates: will expire after 21571 seconds.
fedora: will expire after 604776 seconds.
zammad: will expire after 172798 seconds.
repo: using cache for: updates
not found deltainfo for: Fedora 26 - x86_64 - Updates
updates: using metadata from Thu Oct 26 11:48:06 2017.
repo: using cache for: fedora
not found deltainfo for: Fedora 26 - x86_64
not found updateinfo for: Fedora 26 - x86_64
fedora: using metadata from Wed Jul  5 20:31:38 2017.
repo: using cache for: zammad
Traceback (most recent call last):
  File "/usr/bin/dnf", line 58, in <module>
    main.user_main(sys.argv[1:], exit_code=True)
  File "/usr/lib/python3.6/site-packages/dnf/cli/main.py", line 179, in user_main
    errcode = main(args)
  File "/usr/lib/python3.6/site-packages/dnf/cli/main.py", line 64, in main
    return _main(base, args, cli_class, option_parser_class)
  File "/usr/lib/python3.6/site-packages/dnf/cli/main.py", line 99, in _main
    return cli_run(cli, base)
  File "/usr/lib/python3.6/site-packages/dnf/cli/main.py", line 115, in cli_run
    cli.run()
  File "/usr/lib/python3.6/site-packages/dnf/cli/cli.py", line 1011, in run
    return self.command.run()
  File "/usr/lib/python3.6/site-packages/dnf/cli/commands/makecache.py", line 55, in run
    return self.base.update_cache(self.opts.timer is not None)
  File "/usr/lib/python3.6/site-packages/dnf/base.py", line 298, in update_cache
    self.fill_sack(load_system_repo=False, load_available_repos=True)  # performs the md sync
  File "/usr/lib/python3.6/site-packages/dnf/base.py", line 326, in fill_sack
    self._add_repo_to_sack(r)
  File "/usr/lib/python3.6/site-packages/dnf/base.py", line 122, in _add_repo_to_sack
    hrepo.filelists_fn = repo._filelists_fn
TypeError: Expected a string or a unicode object

Note: repo._filelists_fn is None at this point.

yum-deprecated (3.4.3) output:

# yum-deprecated makecache
Yum command has been deprecated, use dnf instead.
See 'man dnf' and 'man yum2dnf' for more information.

fedora/26/x86_64/metalink                                |  26 kB  00:00:00
updates/26/x86_64/metalink                               |  17 kB  00:00:00
zammad/x86_64/signature                                  |  473 B  00:00:00
zammad/x86_64/signature                                  |  578 B  00:00:00
Error: requested datatype filelists not available