Can't find error in Attempt to read property "ID" on null

It's a classic error, but i just can't seem to find the bug.

I am trying to submit my form:

    <form action="{{ route("doBooking") }}">
        @csrf
        <input type="hidden" name="user_id" id="user_id_value" value="{{$user->id}}">
        <input type="hidden" name="room_id" id="room_id_value">
        <input type="hidden" name="start_time" id="start_time_value">
        <input type="hidden" name="end_time" id="end_time_value">
        <button type="submit">
        </button>
    </form>

I am capturing all of the information just fine here. But i can't submit it. When i try, i'll get an "Attempt to read property "id" on null"-error, and it specifically marks this part of my code:

 $bookings = Booking::where('room_id', $selectedRoom->id)->get(); 

This is what i have inside my user_booking function in my controller:

public function user_booking(Request $request, $id)
{
    $rooms = Room::all();
    $user = User::findOrFail($id);
    $weekdays = WeekdayFactory::getWeekFromDate(new Carbon()); 
    $selectedRoom = Room::find($request->query('room_number')); 
    $bookings = Booking::where('room_id', $selectedRoom->id)->get(); 

    return view('booking.home')->with([
        'weekdays'     => $weekdays,
        'user'         => $user,
        'rooms'        => $rooms,
        'roomSelector' => $selectedRoom,
        'bookings'     => $bookings
    ]);
}

I have tried to dd $selectedRoom and $bookings, and both contains information just fine.

This is what i have inside my user_booking function in my controller:

public function user_booking(Request $request, $id)
{
    $rooms = Room::all();
    $user = User::findOrFail($id);
    $weekdays = WeekdayFactory::getWeekFromDate(new Carbon()); 
    $selectedRoom = Room::find($request->query('room_number')); 
    $bookings = Booking::where('room_id', $selectedRoom->id)->get(); 

    return view('booking.home')->with([
        'weekdays'     => $weekdays,
        'user'         => $user,
        'rooms'        => $rooms,
        'roomSelector' => $selectedRoom,
        'bookings'     => $bookings
    ]);
}

Lastly, if it is any help, this is what i have inside my doBooking function:

public function doBooking(Request $request)
{
    $validatedData = $request->validate([
        'user_id'    => 'required',
        'room_id'    => 'required',
        'start_time' => 'required|before:end_time',
        'end_time'   => 'required|after:start_time',
    ]);

    $bookings = Booking::all();
    foreach ($bookings as $booking) {
        if ($booking->room_id == $validatedData['room_id']) {
            $validateBooking = Booking::whereBetween('start_time', [$validatedData['start_time'], $validatedData['end_time']])
                ->orWhereBetween('end_time', [$validatedData['start_time'], $validatedData['end_time']])
                ->exists();
            if (!$validateBooking) {
                Booking::create($validatedData);
            } else {
                return redirect()->back();
            }
        }
    }
    return view('/');
}

Oh yes, and i have controlled that my route exists, and it looks like this:

Route::post('/booking/create', [BookingsController::class, 'doBooking'])->name('doBooking');