Editor Script no longer working after importing to second project

Hello. I have made an editor script that allows users to click in the scene view and draw lines. It was working perfectly in one project, although I've since tried to incorporate it with a second project, and it has stopped working. Below is the bare bones of the script. I'd be grateful if anyone has any ideas/suggestions.

 using UnityEngine;
 using UnityEditor;
 using System.Collections;
 using System.Collections.Generic;
 
 public class EditorClass : Editor {
     
     void OnEnable() {
         SceneView.onSceneGUIDelegate += SceneGUI;
     }
     
     void SceneGUI(SceneView sceneView) {
         SceneView.RepaintAll();
         
         if (Event.current.type == EventType.layout)
             HandleUtility.AddDefaultControl(GUIUtility.GetControlID(GetHashCode(), FocusType.Passive));
         
         if (Event.current.type == EventType.mouseDown) {
             //Do stuff...
         }
         else if (Event.current.type == EventType.keyDown)
             //Do stuff
         else if (Event.current.type == EventType.mouseMove)
             //Do stuff
     }
 }