Custom relationship eager constraint problem

gistfile1.txt

BadMethodCallException in Builder.php line 2431:
Call to undefined method Illuminate\Database\Query\Builder::getKeys()

Room.php

<?php namespace App\Rooms;

// ...

class Room extends Model
{
    use Locatable, HasCustomRelations;
    
    // ...

    public function occupants()
    {
        return $this->custom(
            User::class,
            // add constraints
            function($relation) {
                $relation->getQuery()
                    ->join('locations', 'users.id', '=', 'locations.locatable_id')
                    ->where([
                        ['locations.locatable_type', User::class],
                        ['locations.parent_id', $this->location->id],
                    ]);
            },
            // add eager constraints
            function($relation, $models) {
                $relation->getQuery()->whereIn('users.id', $relation->getKeys($models));
            }
        );
    }
}

RoomController.php

<?php namespace App\Http\Controllers;

// ...

class RoomController extends Controller
{
    public function index()
    {
        return \App\Rooms\Room::with('occupants')->get();
    }
}