Stack with resource OS::Neutron::Port could not be created when ip_address attr is not specified in fixed_ips property

Stack with resource OS::Neutron::Port could not be created when ip_address attr is not specified in fixed_ips property. From Neutron point of view, attribute ip_address of property fixed_ips is not required and can be ommited.

Steps to Reproduce:
1) Create template:
{
    "AWSTemplateFormatVersion": "2010-09-09",

    "Resources": {
        "port1": {
            "Type": "OS::Neutron::Port",
            "Properties": {
                "network_id": "9a456c59-85d2-4418-92db-a6940944cf99",
                "fixed_ips": [
                    {
                        "subnet_id": "private-subnet"
                    }
                ]
            },
            "Outputs": {
            }
        }
    }
}
2)Try to Launch this template

Expected result:
New port is created and available in Neutron

Observed result:
DEBUG neutronclient.v2_0.client [-] Error message: {"NeutronError": "Invalid input for fixed_ips. Reason: 'None' is not a valid IP address."} from (pid=798) _handle_fault_response /opt/stack/python-neutronclient/neutronclient/v2_0/client.py:1072