EditorGUILayout.ObjectField does not allow me to select a script.

I am trying to make a custom editor window to make a node-editor for the AI in my game. Currently the nodes themselves are displaying nicely (with one or two little bugs), but the object fields I have on each node aren't working. I have a base class script called "State" which is meant to represent an AI State:

 [System.Serializable]
     public class State : ScriptableObject
     {
         public StateIDs _id;
         [SerializeField]private List<TransitionBase> _availableTransitions;
         //some irrelevent code
     }

and then the node is a class which looks like this:

 namespace Assets._Custom._Scripts._Editor
 {
     [System.Serializable]
     public class Node
     {
         public int _id;
         public Rect _box;
         public State _state;
         public FSMNodeEditor _owner;
         
         public Node(int ID, Rect rect, State initState, FSMNodeEditor owner)
         {
             _id = ID;
             _box = rect;
             _state = initState;
             _owner = owner;
         }
             
         public Node(int ID, Rect rect, FSMNodeEditor owner)
         {
             _id = ID;
             _box = rect;    
             _state = (State)ScriptableObject.CreateInstance(typeof(State));
             _owner = owner;
         }
             
         public Node(Rect rect, FSMNodeEditor owner)
         {
             _id = 0;
             _box = rect;
             _state = (State)ScriptableObject.CreateInstance(typeof(State));
             _owner = owner;
         }
             
         public Node(FSMNodeEditor owner)
         {
             _id = 0;
             _box = new Rect();
             _state = (State)ScriptableObject.CreateInstance(typeof(State));
             _owner = owner;
         }
         
         public void DrawNode(int id)
         {
             EditorGUILayout.ObjectField(_state, typeof(State), false);
             
             if(id != _id)
             {
                 Debug.LogError("Given ID and Node ID do not match");
                 
                 return;
             }
             
             if(GUILayout.Button("Join Node"))
             {
                 _owner.JoinNode(id);
             }
             
             if(GUILayout.Button("Delete Node"))
             {
                 _owner.NodeDeleted(id);
             }
 
             GUI.DragWindow();
         }
     }
 }

As you can see, I am trying to use EditorGUILayout.ObjectField to enable me to choose a State to edit in that Node. Problem is, when I create a node in the editor window and click on the button on the object field, no States pop up. There is nothing to choose. I tried making a "TestState" derived from the base State class, but no luck. It just says "None" when I try to choose a State. I even tried dragging TestState onto the object field, but it didn't let me put it in there.

So what is going wrong? Is it because State is a ScriptableObject?

Thank you for any help.