Tempest Rhel7: subnet configures with 0.0.0.0 when sending gateway None

Build: Rhel7 2.20-65~juno

Tempest Case: tempest.api.network.test_networks.NetworksIpV6TestJSON.test_create_list_subnet_with_no_gw64_one_network

As a part of this case, when subnet is created with gateway=None, it gets configured with gateway == 0.0.0.0 which is unacceptable.

Posted Body:
        Body: {"subnet": {"ip_version": 4, "network_id": "cfc8734b-9854-4545-8dea-a52ac2510897", "cidr": "10.100.0.0/28", "gateway_ip": null}}

Received Body:
 Body: {"subnet": {"name": "", "enable_dhcp": true, "network_id": "cfc8734b-9854-4545-8dea-a52ac2510897", "tenant_id": "13df8b8a797440fb95b93cc0053881ec", "dns_nameservers": [], "ipv6_ra_mode": null, "allocation_pools": [{"start": "10.100.0.1", "end": "10.100.0.14"}], "gateway_ip": "0.0.0.0", "ipv6_address_mode": null, "ip_version": 4, "host_routes": [], "cidr": "10.100.0.0/28", "id": "37efd20d-3db4-4066-9ad6-7b299d1f3e90"}}
}}}

Via CLI:

[root@b4s10 ~(keystone_admin)]# neutron subnet-create np-test-net --name np-test-subnet --no-gateway 10.5.5.0/24
Created a new subnet:
+-------------------+--------------------------------------------+
| Field | Value |
+-------------------+--------------------------------------------+
| allocation_pools | {"start": "10.5.5.1", "end": "10.5.5.254"} |
| cidr | 10.5.5.0/24 |
| dns_nameservers | |
| enable_dhcp | True |
| gateway_ip | 0.0.0.0 |
| host_routes | |
| id | e5668218-8388-4542-83d0-ad156082ccf6 |
| ip_version | 4 |
| ipv6_address_mode | |
| ipv6_ra_mode | |
| name | np-test-subnet |
| network_id | d81221e8-c5c5-417d-823d-7368b651ee28 |
| tenant_id | 13df8b8a797440fb95b93cc0053881ec |
+-------------------+--------------------------------------------+
[root@b4s10 ~(keystone_admin)]#