Set default length for an array of elements of a custom class in inspector

I'm making a game set on a five-lane road and I want to create a scriptable object that can be used to rapidly create new patterns of traffic.

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 [CreateAssetMenu(fileName = "New Vehicle Set", menuName = "ScriptableObjects/Vehicle Set", order = 1)]
 public class VehicleSet : ScriptableObject
 {
     public enum VehicleType {none, car, truck, coin}
 
     [System.Serializable]
     public class VehicleRow
     {
         public VehicleType[] rowVehicles = new VehicleType[5];
         public int[] test = new int[5];
 
         public VehicleRow()
         {
             rowVehicles = new VehicleType[5];
             for (int i = 0;i<5;i++)
             {
                 rowVehicles[i] = VehicleType.none;
             }
         }
     }
 
     public VehicleRow[] vehicles;
 }
 

Right now, when i create a new instance of VehicleSet, it shows me the list of VehicleRows (which is initially empty) and i can add new rows.

While the int array initializes correctly with 5 elements, the VehicleType one is initially empty. How do I instruct the editor to initialize the array with a length of 5?