facter fails to report correct ipaddress when routing_table fails on default gateway entry

The routing table is as follows:
default via XXX.XXX.XXX.XXX dev ens3 onlink
10.42.0.0/16 dev docker0 proto kernel scope link src 10.42.0.1
XXX.XXX.XXX.XXX/24 dev ens3 proto kernel scope link src XXX.XXX.XXX.XXX
172.17.0.0/16 dev docker0 proto kernel scope link src 172.17.0.1

facter fails to parse the default via line due to onlink (FACT-1405) logging a warning.

Thus fails to detect the primary_interface and thus returns the first interface it finds namely "docker0" which returns the same IP for every host. (and causes issues with exported resources using ipaddress in our case – sshkey)

I tried reading the code to find out what happens but could not reach a conclusion.

From what I can see, there are two possible ways to parse the routing table, the first is by reading the output of "ip route show" in
./lib/src/facts/linux/networking_resolver.cc:123 void networking_resolver::read_routing_table()

Which actually makes the warning, the other is by parsing "/proc/net/route" in
./lib/src/facts/linux/networking_resolver.cc:97 string networking_resolver::get_primary_interface() const

But I could not find where it is called. In solaris implementation it is called directly in the same file, so my guess is that this function might not be used at all. Too bad, since with this function (without the check in line 102 "if (routes4.size()) {"), it would work correctly.