Trying to add a prefab to a list that i can edit in the inspector. All other items work.

  for (int i = 0; i < dwarven.Count; i++)
             {
                 EditorGUILayout.BeginHorizontal();
                 EditorGUILayout.LabelField(dwarven[i].name);
 
                 if (GUILayout.Button("-"))
                     cm.cardList.Remove(dwarven[i]);
                 EditorGUILayout.EndHorizontal();
 
                 EditorGUI.indentLevel += 1;
                 dwarven[i].name = EditorGUILayout.TextField("Name: ", dwarven[i].name);
                 dwarven[i].ID = int.Parse(EditorGUILayout.TextField("ID: ", dwarven[i].ID.ToString()));
                 dwarven[i].Cost = int.Parse(EditorGUILayout.TextField("Cost: ", dwarven[i].Cost.ToString()));
                dwarven[i].cardPrefab = EditorGUILayout.ObjectField("Card Prefab: ", GameObject.cardPrefab, typeof(GameObject));
                
                // i've also tried
                 //Card.cardPrefab = (GameObject)EditorGUILayout.ObjectField("Card Prefab:", dwarven[i].cardPrefab, typeof(GameObject), true);
 
                 EditorGUI.indentLevel -= 1;
                 EditorGUILayout.Space();
             } 
 
             if (GUILayout.Button("Add New Card"))
             {
                 Dwarven newDwarven = CreateInstance<Dwarven>();
                 newDwarven.name = "";
                 newDwarven.ID = 0;
                 newDwarven.Cost = 0;
                 newDwarven.cardPrefab = cardPrefab as GameObject;
                 cm.cardList.Add(newDwarven);
             }
             EditorGUI.indentLevel = 0;