Patch [1] merged and we have support to run fc29 on mock with mirrors.

[1]: https://gerrit.ovirt.org/#/c/96595/

great! please update if it works.

Thanks for the hint! I've looked at the code and created a simple patch that re-introduces parsing of none values. Sent a pull request upstream:

https://github.com/rpm-software-management/dnf/pull/1300

Also patched DNF manually on vm0150 attached to the Staging Jenkins so let's see how CI performs there as it should run el7 patches fine now

Might be this line:
"""Handles string values where only specific values are allowed."""
def _init_(self, default=None):

Thanks for the clarification. Looks like DNF switched to a C++ implementation of the parser in version 3.0.1. Before that (Fedora 28 still has version 2.7.5 for instance) it was using legacy code from yum which had the check but was removed.

To be honest I don't see a reason in changing this parsing behavior. I can't read C++ code so can't pin-point the place where new functionality is present in the parser but worth opening a bug.