Why isn't my CustomEditor's OnInspectorGUI() running?

Hi,

I hope someone can help. I've been scouring the forums, working on a solution and I think I'm just missing something. The OnInspectorGUI in my CustomEditor is never being run. I placed a breakpoint inside and it doesn't get hit. Here's my code. Any advice is GREATLY appreciated!

 using System;
 using UnityEngine;
 using UnityEditor;
 
 [CustomEditor(typeof(Row))]
 public class RowEditor : Editor {
 
     bool toggle1, toggle2, toggle3, toggle4;
 
     public override void OnInspectorGUI() {
         GUILayoutOption toggleOption = GUILayout.Width (EditorGUIUtility.currentViewWidth / 4);
         EditorGUILayout.BeginHorizontal ();
         toggle1 = EditorGUILayout.Toggle ("", toggle1, toggleOption);
         toggle2 = EditorGUILayout.Toggle ("", toggle2, toggleOption);
         toggle3 = EditorGUILayout.Toggle ("", toggle3, toggleOption);
         toggle4 = EditorGUILayout.Toggle ("", toggle4, toggleOption);
         EditorGUILayout.EndHorizontal ();
     }
 }

 using System;
 using UnityEngine;
 
 [Serializable]
 public class Row : ScriptableObject {
 
     public bool track1;
     public bool track2;
     public bool track3;
     public bool track4;
 
 }

 using UnityEngine;
 using System.Collections;
 
 public class SpawnManager : MonoBehaviour {
 
     public Row spawnRow;
 
 }