MissingReferenceException: The object of type 'InventoryItemSetManager' has been destroyed but you are still trying to access it.
Your script should either check if it is null or you should not destroy the object.
UnityEngine.Component.GetComponent[T] () (at <10564ed154d647e194bef4aef8878649>:0)
Opsive.UltimateCharacterController.Integrations.UltimateInventorySystem.Editor.InventoryItemSetManagerInspector.CreateInspectorGUI () (at Assets/Opsive/UltimateCharacterController/Integrations/UltimateInventorySystem/Editor/InventoryItemSetManagerInspector.cs:48)
UnityEditor.UIElements.InspectorElement.CreateInspectorElementFromEditor (UnityEditor.Editor editor, System.Boolean reuseIMGUIContainer) (at <0fdaf67e8e744beea25e77915c19f81b>:0)
UnityEditor.UIElements.InspectorElement.Reset (UnityEditor.SerializedObject bindObject) (at <0fdaf67e8e744beea25e77915c19f81b>:0)
UnityEditor.UIElements.InspectorElement.ExecuteDefaultActionAtTarget (UnityEngine.UIElements.EventBase evt) (at <0fdaf67e8e744beea25e77915c19f81b>:0)
UnityEngine.UIElements.CallbackEventHandler.HandleEvent (UnityEngine.UIElements.EventBase evt) (at <1cdf5c2cc10149169242b9590b7ebb6b>:0)
UnityEngine.UIElements.CallbackEventHandler.HandleEventAtTargetPhase (UnityEngine.UIElements.EventBase evt) (at <1cdf5c2cc10149169242b9590b7ebb6b>:0)
UnityEditor.UIElements.Bindings.SerializedObjectBindingContext.SendBindingEvent[TEventType] (TEventType evt, UnityEngine.UIElements.VisualElement target) (at <0fdaf67e8e744beea25e77915c19f81b>:0)
UnityEditor.UIElements.Bindings.SerializedObjectBindingContext.BindTree (UnityEngine.UIElements.VisualElement element, UnityEditor.SerializedProperty parentProperty) (at <0fdaf67e8e744beea25e77915c19f81b>:0)
UnityEditor.UIElements.Bindings.SerializedObjectBindingContext.ContinueBinding (UnityEngine.UIElements.VisualElement element, UnityEditor.SerializedProperty parentProperty) (at <0fdaf67e8e744beea25e77915c19f81b>:0)
UnityEditor.UIElements.Bindings.SerializedObjectBindingContext.Bind (UnityEngine.UIElements.VisualElement element) (at <0fdaf67e8e744beea25e77915c19f81b>:0)
UnityEditor.UIElements.Bindings.DefaultSerializedObjectBindingImplementation.Bind (UnityEngine.UIElements.VisualElement element, UnityEditor.SerializedObject obj) (at <0fdaf67e8e744beea25e77915c19f81b>:0)
UnityEditor.UIElements.BindingExtensions.Bind (UnityEngine.UIElements.VisualElement element, UnityEditor.SerializedObject obj) (at <0fdaf67e8e744beea25e77915c19f81b>:0)
UnityEditor.UIElements.InspectorElement..ctor (UnityEditor.Editor editor, UnityEditor.UIElements.InspectorElement+Mode mode) (at <0fdaf67e8e744beea25e77915c19f81b>:0)
UnityEditor.UIElements.EditorElement.Init () (at <0fdaf67e8e744beea25e77915c19f81b>:0)
UnityEditor.UIElements.EditorElement..ctor (System.Int32 editorIndex, UnityEditor.IPropertyView iw, System.Boolean isCulled) (at <0fdaf67e8e744beea25e77915c19f81b>:0)
UnityEditor.EditorUIServiceImpl.CreateEditorElement (System.Int32 editorIndex, UnityEditor.IPropertyView iw, System.String title) (at <5f5866ec908d4054a9597064f39dbbac>:0)
UnityEditor.PropertyEditor.DrawEditors (UnityEditor.Editor[] editors) (at <d6a6a4b561b9431dbfe2c61f7bf0d405>:0)
UnityEditor.PropertyEditor.RebuildContentsContainers () (at <d6a6a4b561b9431dbfe2c61f7bf0d405>:0)
UnityEditor.InspectorWindow.RedrawFromNative () (at <d6a6a4b561b9431dbfe2c61f7bf0d405>:0)