ScriptableObject does not serialize

For some reason, my ScriptableObject does not save the list I have on it. I am trying to make a database. I tried everything to fix it, even copied the code from my older project(SO work properly there), but still nothing happens. This is the ScriptableObject script:

 public class TestEnemyDatabase : ScriptableObject {
 
     [SerializeField]
     List<TestEnemyScript> database = new List<TestEnemyScript>();
 
     public void Add(TestEnemyScript enemy) {
         database.Add (enemy);
     }
         
 }

Item class:

 [System.Serializable]
 public class TestEnemyScript {
 
     [SerializeField]
     int _damage;
 
     [SerializeField]
     float _health;
 
     public TestEnemyScript(int dmg, float hp) {
         _damage = dmg;
         _health = hp;
     }
 
     public int Damage {
         get { return _damage; }
         set { _damage = value; }
     }
 
     public float Health {
         get { return _health; }
         set { _health = value; }
     }
 
 }

And the Editor Script:

 public class TestDatabaseEditor : EditorWindow {
 
     int newDamage;
     float newHealth;
 
     private TestEnemyDatabase enemyDatabase;
 
     private const string DATABASE_PATH = "Assets/TestDatabase.asset";
 
     [MenuItem("Window/Test Enemy Database")]
     public static void ShowWindow() {
         EditorWindow window = EditorWindow.GetWindow (typeof(TestDatabaseEditor));
         window.Show ();
     }
 
     void OnEnable() {
         if (enemyDatabase == null) {
             LoadDatabase ();
         }
     }
 
     void LoadDatabase() {
         enemyDatabase = (TestEnemyDatabase)AssetDatabase.LoadAssetAtPath (DATABASE_PATH, typeof(TestEnemyDatabase));
 
         if (enemyDatabase == null) {
             CreateDatabase ();
         }
     }
 
     void CreateDatabase() {
         // Debug.Log ("New Enemy Database has been created.");
 
         enemyDatabase = ScriptableObject.CreateInstance<TestEnemyDatabase> ();
         AssetDatabase.CreateAsset (enemyDatabase, DATABASE_PATH);
         AssetDatabase.SaveAssets ();
         AssetDatabase.Refresh ();
     }
 
     void OnGUI() {
         newDamage = EditorGUILayout.IntField ("Damage: ", newDamage);
         newHealth = EditorGUILayout.FloatField ("Health: ", newHealth);
 
         if (GUILayout.Button("Add a new item")) {
             // TestEnemyScript enemyScript = new TestEnemyScript (newDamage, newHealth);
 
             enemyDatabase.Add (new TestEnemyScript (newDamage, newHealth));
         }
     }
 }