[2.x, API] Unable to update iprange user by name via API

The IP range form erroneously expects a user ID, which is not easily available.

$ maas admin iprange update 7 user=user
{"user": ["Select a valid choice. That choice is not one of the available choices."]}

$ sudo -u postgres psql maasdb -c "select id from auth_user where username='user'"
 id
----
  4
(1 row)

$ maas admin iprange update 7 user=4
Success.
Machine-readable output follows:
{
    "resource_uri": "/MAAS/api/2.0/ipranges/7/",
    "id": 7,
    "user": {
        "resource_uri": "/MAAS/api/2.0/users/user/",
        "username": "user",
        "is_superuser": false,
        "email": "<email address hidden>"
    },
    "start_ip": "192.168.0.201",
    "end_ip": "192.168.0.249",
    "subnet": {
        "rdns_mode": 2,
        "id": 8,
        "active_discovery": false,
        "vlan": {
            "fabric": "fabric-0",
            "id": 5001,
            "relay_vlan": null,
            "resource_uri": "/MAAS/api/2.0/vlans/5001/",
            "mtu": 1500,
            "secondary_rack": null,
            "name": "untagged",
            "fabric_id": 0,
            "vid": 0,
            "primary_rack": null,
            "space": "undefined",
            "external_dhcp": "192.168.122.1",
            "dhcp_on": false
        },
        "resource_uri": "/MAAS/api/2.0/subnets/8/",
        "allow_proxy": true,
        "name": "192.168.0.0/24",
        "cidr": "192.168.0.0/24",
        "space": "undefined",
        "gateway_ip": null,
        "dns_servers": [],
        "managed": true
    },
    "comment": "",
    "type": "reserved"
}