Can't load HealthEditor

[tacman]

In both 2019.4 and 2020.1 (latest versions), I get this error when following the instructions in the video at

https://www.youtube.com/watch?v=2_UY_RBEVLQ

New 3D project, Add UI Builder, Import from github this repo, import HealthEffects, open ExampleScene, click on Player.

Any suggestions? Unity seems very sensitive, would love to figure out what the issue is. Thanks.

NullReferenceException: Object reference not set to an instance of an object
Example.Scripts.Player.Monobehaviours.Editor.HealthEditor.CreateInspectorGUI () (at Assets/Samples/Tween Library/1.0.3/Healthbar Effects/Scripts/Player/Monobehaviours/Editor/HealthEditor.cs:33)
UnityEditor.UIElements.InspectorElement.CreateInspectorElementFromEditor (UnityEditor.Editor editor, System.Boolean reuseIMGUIContainer) (at /home/bokken/buildslave/unity/build/Editor/Mono/Inspector/InspectorElement.cs:598)
UnityEditor.UIElements.InspectorElement.Reset (UnityEditor.SerializedObject bindObject) (at /home/bokken/buildslave/unity/build/Editor/Mono/Inspector/InspectorElement.cs:232)
UnityEditor.UIElements.InspectorElement.ExecuteDefaultActionAtTarget (UnityEngine.UIElements.EventBase evt) (at /home/bokken/buildslave/unity/build/Editor/Mono/Inspector/InspectorElement.cs:272)
UnityEngine.UIElements.CallbackEventHandler.HandleEvent (UnityEngine.UIElements.EventBase evt) (at /home/bokken/buildslave/unity/build/Modules/UIElements/Events/EventHandler.cs:106)
UnityEngine.UIElements.CallbackEventHandler.HandleEventAtTargetPhase (UnityEngine.UIElements.EventBase evt) (at /home/bokken/buildslave/unity/build/Modules/UIElements/Events/EventHandler.cs:79)
UnityEditor.UIElements.BindingExtensions.SendBindingEvent[TEventType] (TEventType evt, UnityEngine.UIElements.VisualElement target) (at /home/bokken/buildslave/unity/build/Editor/Mono/UIElements/Controls/BindingExtensions.cs:210)
UnityEditor.UIElements.BindingExtensions.Bind (UnityEngine.UIElements.VisualElement element, UnityEditor.UIElements.BindingExtensions+SerializedObjectUpdateWrapper objWrapper, UnityEditor.SerializedProperty parentProperty) (at /home/bokken/buildslave/unity/build/Editor/Mono/UIElements/Controls/BindingExtensions.cs:168)
UnityEditor.UIElements.BindingExtensions.Bind (UnityEngine.UIElements.VisualElement element, UnityEditor.SerializedObject obj) (at /home/bokken/buildslave/unity/build/Editor/Mono/UIElements/Controls/BindingExtensions.cs:94)
UnityEditor.UIElements.InspectorElement..ctor (UnityEditor.Editor editor, UnityEditor.UIElements.InspectorElement+Mode mode) (at /home/bokken/buildslave/unity/build/Editor/Mono/Inspector/InspectorElement.cs:153)
UnityEditor.UIElements.EditorElement.Init () (at /home/bokken/buildslave/unity/build/Editor/Mono/Inspector/EditorElement.cs:109)
UnityEditor.UIElements.EditorElement..ctor (System.Int32 editorIndex, UnityEditor.InspectorWindow iw) (at /home/bokken/buildslave/unity/build/Editor/Mono/Inspector/EditorElement.cs:86)
UnityEditor.InspectorWindow.DrawEditors (UnityEditor.Editor[] editors) (at /home/bokken/buildslave/unity/build/Editor/Mono/Inspector/InspectorWindow.cs:1680)
UnityEditor.InspectorWindow.RebuildContentsContainers () (at /home/bokken/buildslave/unity/build/Editor/Mono/Inspector/InspectorWindow.cs:763)
UnityEditor.InspectorWindow.RedrawFromNative () (at /home/bokken/buildslave/unity/build/Editor/Mono/Inspector/InspectorWindow.cs:352)