docker-compose正在创建没有默认网关的网络

Question

[
    {
        "Name": "thesis_default",
        "Id": "9687111d5ffd8823b7e63f52b0acc700ed876345b386498b1805b2384ad89cd3",
        "Created": "2019-05-03T16:22:16.50673158+03:00",
        "Scope": "local",
        "Driver": "bridge",
        "EnableIPv6": false,
        "IPAM": {
            "Driver": "default",
            "Options": null,
            "Config": [
                {
                    "Subnet": "172.20.0.0/16"
                }
            ]
        },
        "Internal": false,
        "Attachable": true,
        "Ingress": false,
        "ConfigFrom": {
            "Network": ""
        },
        "ConfigOnly": false,
        "Containers": {},
        "Options": {},
        "Labels": {
            "com.docker.compose.network": "default",
            "com.docker.compose.project": "thesis",
            "com.docker.compose.version": "1.24.0"
        }
    }
]

从上面可以看到docker-compose正在创建没有默认网关的网络。

docker-compose.yml在此处https://github.com/victortodoran/magento2-docker/blob/master/docker-compose.yml

我的docker版本是18.09.5。我的docker-compose版本是1.24.0。我的操作系统是Ubuntu 16.04。

有人知道为什么会这样吗？为什么我没有为我的网络设置默认网关？