Why this error using Firestore get() method? ERROR TypeError: snaps.map is not a function

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I am working on an Angular project using Firebase FireStore database and I implemented this method to perform a query:

  findArtistBidsAppliedByCurrentWall(bid):Observable<Bid[]> {
    console.log("findArtistBidsAppliedByCurrentWall() START")
    return this.db.collection('bids',
        ref=> ref.where("wallId", "==", bid.wallId))
        .get()
        .pipe(
            map(snaps => {
                console.log("TEST");
                const bids = this.convertSnaps<Bid>(snaps);

                return bids;
            })
        )
  }

NOTE: I have to use get() and not snapshotChanges() in order to not listen to changes.

The problem is that when the previous code is excecuted I obtain the following error message into the browser developer tools:

ERROR TypeError: snaps.map is not a function
    convertSnaps notifications.service.ts:185
    findArtistBidsAppliedByCurrentWall notifications.service.ts:159
    RxJS 4
    Angular 6
    RxJS 3
    Angular 16
    RxJS 4
    schedule Angular
    RxJS 4
    Angular 20
    node_modules vendor.js:157356
    node_modules NextJS
    node_modules vendor.js:149711
    node_modules vendor.js:149679
    Ur index.cjs.js:5711
    Us index.cjs.js:11891
    step tslib.es6.js:100
    verb tslib.es6.js:81
    fulfilled tslib.es6.js:71
    Angular 13
        invoke
        run
        scheduleResolveOrReject
        invokeTask
        runTask
        drainMicroTaskQueue
        invokeTask
        invokeTask
        globalZoneAwareCallback
        customScheduleGlobal
        scheduleTask
        scheduleTask
        scheduleEventTask
core.js:6241:19
    Angular 4
    RxJS 5
    Angular 20
    RxJS 12
    Angular 6
    RxJS 3
    Angular 16
    RxJS 4
    schedule Angular
    RxJS 4

why this error? What is wrong? What am I missing?

Source: Angular Questions