Bad error when interest room prefixes are not configured but existing interest rooms are

[reivilibre]

Given

    "existingInterestRooms": {
      "I.infodesk": "#infodesk:fosdem.org"
    },
    "prefixes": {
      "interestRooms": [],
...

It seems like this block of code:

        // Resolve pre-existing interest rooms
        for (const interestId in config.conference.existingInterestRooms) {
            if (interestId in this.interestRooms) {
                continue;
            }

            const roomIdOrAlias = config.conference.existingInterestRooms[interestId];
            let roomId: string;
            try {
                roomId = await this.client.resolveRoom(roomIdOrAlias);
            } catch (e) {
                // The room probably doesn't exist yet.
                continue;
            }

            this.interestRooms[interestId] = new InterestRoom(roomId, this.client, this, interestId); // <---
        }

causes an issue in the InterestRoom constructor:

this.name = decodePrefix(id, config.conference.prefixes)!.name; // <---

Wed, 01 Feb 2023 15:03:21 GMT [ERROR] [index] Fatal error TypeError: Cannot read property 'name' of null
    at new InterestRoom (/app/lib/models/InterestRoom.js:32:98)
    at Conference.construct (/app/lib/Conference.js:215:46)
    at runMicrotasks (<anonymous>)
    at processTicksAndRejections (internal/process/task_queues.js:95:5)
    at async /app/lib/index.js:106:5

Maybe it's ill-defined to have the config like this but it would be nice if this was at least reported better rather than wasting time figuring it out — particularly as there's another invocation of the constructor which looks like the likely culprit but isn't.