phpvms/app/Models/Traits/Expensable.php

<?php

namespace App\Models\Traits;

use App\Models\Expense;

trait Expensable
{
    public static function bootExpensable()
    {

    }

    /**
     * Morph to Expenses.
     * @return mixed
     */
    public function expenses()
    {
        return $this->morphMany(
            Expense::class,
            'expenses',  # overridden by the next two anyway
            'ref_class',
            'ref_class_id'
        );
    }
}