First time daemon is booted (no docker0 bridge present, no or empty /var/lib/docker/network/files/local-kv.db file), IPAM.Config structure in network inspect output will not contain the Gateway field

$ docker network inspect bridge
[
    {
        "Name": "bridge",
        "Id": "2b5cc5f97b6de6a5e0533b1e2d5bec6284d900a9a82632ce782320a19db8b9e0",
        "Scope": "local",
        "Driver": "bridge",
        "EnableIPv6": false,
        "IPAM": {
            "Driver": "default",
            "Options": null,
            "Config": [
                {
                    "Subnet": "172.17.0.0/16"
                }
            ]
        },

Verified problem exists in 1.11.2, 1.12.0 and in current master (1.13.0).

Given the IPAM.Config filed currently used to carry both configuration and operational data, the gateway address should always be there.

Note:
A daemon reload will fix the issue