Problem with added models

Aldebaraan

My mod has a ini where users can define the models that a ped will spawn as:

Ini:
[StormtrooperSpawnSettings]
MaxMembers=2
Accuracy=10
Health=140
BodyArmor=100
OnlyAttackPlayer=false
Models=stormtrooper
Weapons=UnholyHellbringer

with vanilla models it works fine. But in the case of addon models it throws a null exception error.
Here's the code:

private Ped SpawnRandomPed(List<Ped> ListPeds, string[] ModelsList, string[] WeaponsList, int Accuracy, int Health, int BodyArmor, bool OnlyAttackPlayer, bool WillAttackSelf, int RelationshipGroup)
{
string ModelName = RandomChoice<string>(ModelsList);

PedHash pedSpawn;

if (!Enum.TryParse<PedHash>(ModelName, true, out pedSpawn))
{
    throw new FormatException("Ped name " + ModelName + " does not exist!");
}

Vector3 PositionToUse;
RandomDistance = Function.Call<float>(Hash.GET_RANDOM_FLOAT_IN_RANGE, PedMinSpawnDistance, PedMaxSpawnDistance);
PositionToUse = Game.Player.Character.Position.Around(PedMaxSpawnDistance);
		
Ped ped = World.CreatePed(pedSpawn, PositionToUse);

}

How can i make the game recognize the models? When i apply them to my character it works.