LuCI: overview page issue with incorrect /etc/board.json

[rany2]

If your /etc/board.json contains:

{
	<...>
	"network": {
		"lan": {
			"device": "eth0",
			"protocol": "static"
		}
	}
}

but 'eth0' does not exist (for instance, it's 'nic0' on the host instead). The LuCI overview page will not load and errors out with:

Uncaught (in promise) TypeError: can't access property "toString", subst is undefined
    format https://192.168.1.1/luci-static/resources/cbi.js?v=26.179.00003~cf114f9:114
    formatStats https://192.168.1.1/luci-static/resources/view/status/include/29_ports.js?v=26.184.55701~45b3640-1783700718:60
    render https://192.168.1.1/luci-static/resources/view/status/include/29_ports.js?v=26.184.55701~45b3640-1783700718:88
    render https://192.168.1.1/luci-static/resources/view/status/include/29_ports.js?v=26.184.55701~45b3640-1783700718:86
    poll_status https://192.168.1.1/luci-static/resources/view/status/index.js?v=26.184.55701~45b3640-1783700718:7
    promise callback*poll_status https://192.168.1.1/luci-static/resources/view/status/index.js?v=26.184.55701~45b3640-1783700718:4
    render https://192.168.1.1/luci-static/resources/view/status/index.js?v=26.184.55701~45b3640-1783700718:14
cbi.js:114:16
    error https://192.168.1.1/luci-static/resources/luci.js?v=26.184.55701~45b3640-1783700718:159
    (Async: promise callback)
    __init__ https://192.168.1.1/luci-static/resources/luci.js?v=26.184.55701~45b3640-1783700718:140
    super https://192.168.1.1/luci-static/resources/luci.js?v=26.184.55701~45b3640-1783700718:15
    ClassConstructor https://192.168.1.1/luci-static/resources/luci.js?v=26.184.55701~45b3640-1783700718:5
    compileClass https://192.168.1.1/luci-static/resources/luci.js?v=26.184.55701~45b3640-1783700718:176
    (Async: promise callback)
    compileClass https://192.168.1.1/luci-static/resources/luci.js?v=26.184.55701~45b3640-1783700718:172
    (Async: promise callback)
    require https://192.168.1.1/luci-static/resources/luci.js?v=26.184.55701~45b3640-1783700718:178
    instantiateView https://192.168.1.1/luci-static/resources/ui.js?v=26.184.55701~45b3640-1783700718:375
    <anonymous> https://192.168.1.1/cgi-bin/luci/:94
    (Async: promise callback)
    <anonymous> https://192.168.1.1/cgi-bin/luci/:93