Comment 2 for bug 1943481

Yeah, looking at the patch it's clear the NULL setting was accidentally (?) left off:

- if (physPortID) {
- if (firstEntryName) {
- /* we didn't match the provided phys_port_id, but this
- * is probably because phys_port_id isn't implemented
- * for this NIC driver, so just return the first
- * (probably only) netname we found.
- */
- *netname = firstEntryName;
- firstEntryName = NULL;
- ret = 0;
- } else {
- virReportError(VIR_ERR_INTERNAL_ERROR,
- _("Could not find network device with "
- "phys_port_id '%s' under PCI device at %s"),
- physPortID, device_link_sysfs_path);
- }
+ if (firstEntryName) {
+ /* we didn't match the provided phys_port_id / find a
+ * phys_port_name matching VIR_PF_PHYS_PORT_NAME_REGEX / find
+ * as many net devices as the value of idx, but this is
+ * probably because phys_port_id / phys_port_name isn't
+ * implemented for this NIC driver, so just return the first
+ * (probably only) netname we found.
+ */
+ *netname = firstEntryName;
+ ret = 0;

either using g_steal_pointer() or just manually setting firstEntryName = NULL (as the code previously did) should fix things, since firstEntryName is automatically freed at the end of the function (since it's declared with g_autofree).