How to get room name in prosody plugin?

I found some topic talk about this, but I can’t get success by following explanations in those topics.

My environment is setup by docker-jitsi-meet, I did’t modify any configuration except expose http endpoint.

This is what I do in the plugin:

function handle_list_room(event)
    local rooms = {}

    for key, value in pairs(prosody.full_sessions) do
        if tostring(value["username"]:lower()) ~= "focus" then
            table.insert(rooms, tostring(value["jitsi_meet_room"]))

    return json.encode(rooms)

And this is what I get in browser:

[nil, nil, nil]

Can someone help me to get a list of room names?

I found a way to do this.

local mod_muc = module:depends("muc");
function handle_list_rooms(event)
    for room in mod_muc.all_rooms() do
       - ...
    - ...