Router interface port's subnet is null preventing it from being deleted

[Eugene Nikanorov]

For some reason a router got router interface port having subnet as null.
That prevents this port from being deleted and also prevents router from being deleted.

As a result, the network having that port can't be deleted as well.

# neutron port-show 9fe93eda-f682-451c-882f-fa02beafac14
+---------------------+----------------------------------------------+
| Field | Value |
+---------------------+----------------------------------------------+
| admin_state_up | True |
| binding:vif_details | {"port_filter": true} |
| binding:vif_type | vrouter |
| binding:vnic_type | normal |
| device_id | 4ad5eb25-500e-4dd4-88f8-96e9ee2eca76 |
| device_owner | network:router_interface |
| fixed_ips | {"subnet_id": null, "ip_address": "0.0.0.0"} |
| id | 9fe93eda-f682-451c-882f-fa02beafac14 |
| mac_address | 02:9f:e9:3e:da:f6 |
| name | 9fe93eda-f682-451c-882f-fa02beafac14 |
| network_id | 161183d2-49d5-40b0-b441-b109207730ac |
| security_groups | 2d9c798b-b78a-4494-a801-32e85417f4f6 |
| status | ACTIVE |
| tenant_id | 95d18ca0492040ad9e3b9e867bcfb520 |
+---------------------+———————————————————————+

[Shyam Bhople (shyamb)]

Please share exact steps to reproduce this.