With an empty window, pressing the editor pause button throws a null reference error. This happens regardless of being in play mode or not.

*Repro*
# Open the ARC window and leave it in the empty state
# Press pause in the editor

Expected: No error is thrown in the console

Actual: A null reference error is thrown

*Note*

Originally thought to be a regression, but discovered that it was not.
* Reproducible on 2023.2.0b1 and upwards
* NOT Reproducible on 2023.2.0a22 and upwards
* Reproducible on 2023.2.0a21

So 0a22 looks like it could include a fix. Since it was not reproducible on this version it was thought to be a regression, but it was reproduced on 0a21, ruling it out as a regression

*Stack trace*
{code:java}
NullReferenceException: Object reference not set to an instance of an object
UnityEditor.AudioContainerWindow.UpdateTransportButtonStates () (at /Users/kristinnbragi/gitrepo/23.2/Editor/Mono/Audio/AudioContainerWindow.cs:393)
UnityEditor.AudioContainerWindow.EditorPauseStateChanged (System.Object sender, System.EventArgs e) (at /Users/kristinnbragi/gitrepo/23.2/Editor/Mono/Audio/AudioContainerWindow.cs:403)
UnityEditor.AudioContainerWindowState.OnEditorPauseStateChanged (UnityEditor.PauseState state) (at /Users/kristinnbragi/gitrepo/23.2/Editor/Mono/Audio/AudioContainerWindowState.cs:277)
UnityEditor.EditorApplication.Internal_PauseStateChanged (UnityEditor.PauseState state) (at /Users/kristinnbragi/gitrepo/23.2/Editor/Mono/EditorApplication.cs:447)
UnityEditor.EditorApplication:set_isPaused(Boolean)
UnityEditor.Toolbars.PlayModeButtons:OnPauseButtonValueChanged(ChangeEvent`1) (at /Users/kristinnbragi/gitrepo/23.2/Modules/EditorToolbar/ToolbarElements/PlayModeButtons.cs:139)
UnityEngine.UIElements.EventCallbackFunctor`1:Invoke(EventBase) (at /Users/kristinnbragi/gitrepo/23.2/Modules/UIElements/Core/Events/EventCallback.cs:64)
UnityEngine.UIElements.DynamicCallbackList:Invoke(EventBase, BaseVisualElementPanel, VisualElement) (at /Users/kristinnbragi/gitrepo/23.2/Modules/UIElements/Core/Events/EventCallbackRegistry.cs:228)
UnityEngine.UIElements.EventDispatchUtilities:HandleEvent_BubbleUpCallbacks(EventBase, BaseVisualElementPanel, VisualElement) (at /Users/kristinnbragi/gitrepo/23.2/Modules/UIElements/Core/Events/EventDispatchUtilities.cs:385)
UnityEngine.UIElements.EventDispatchUtilities:HandleEventAcrossPropagationPath(EventBase, BaseVisualElementPanel, VisualElement, Boolean) (at /Users/kristinnbragi/gitrepo/23.2/Modules/UIElements/Core/Events/EventDispatchUtilities.cs:183)
UnityEngine.UIElements.EventDispatchUtilities:PropagateEvent(EventBase, BaseVisualElementPanel, VisualElement, Boolean) (at /Users/kristinnbragi/gitrepo/23.2/Modules/UIElements/Core/Events/EventDispatchUtilities.cs:61)
UnityEngine.UIElements.EventDispatchUtilities:DefaultDispatch(EventBase, BaseVisualElementPanel) (at /Users/kristinnbragi/gitrepo/23.2/Modules/UIElements/Core/Events/EventDispatchUtilities.cs:564)
UnityEngine.UIElements.EventBase:Dispatch(BaseVisualElementPanel) (at /Users/kristinnbragi/gitrepo/23.2/Modules/UIElements/Core/Events/EventBase.cs:110)
UnityEngine.UIElements.EventDispatcher:ProcessEvent(EventBase, BaseVisualElementPanel) (at /Users/kristinnbragi/gitrepo/23.2/Modules/UIElements/Core/EventDispatcher.cs:336)
UnityEngine.UIElements.EventDispatcher:ProcessEventQueue() (at /Users/kristinnbragi/gitrepo/23.2/Modules/UIElements/Core/EventDispatcher.cs:291)
UnityEngine.UIElements.EventDispatcher:OpenGate() (at /Users/kristinnbragi/gitrepo/23.2/Modules/UIElements/Core/EventDispatcher.cs:255)
UnityEngine.UIElements.EventDispatcherGate:Dispose() (at /Users/kristinnbragi/gitrepo/23.2/Modules/UIElements/Core/EventDispatcher.cs:78)
UnityEngine.UIElements.EventDispatcher:ProcessEvent(EventBase, BaseVisualElementPanel) (at /Users/kristinnbragi/gitrepo/23.2/Modules/UIElements/Core/EventDispatcher.cs:346)
UnityEngine.UIElements.EventDispatcher:Dispatch(EventBase, BaseVisualElementPanel, DispatchMode) (at /Users/kristinnbragi/gitrepo/23.2/Modules/UIElements/Core/EventDispatcher.cs:200)
UnityEngine.UIElements.BaseVisualElementPanel:SendEvent(EventBase, DispatchMode) (at /Users/kristinnbragi/gitrepo/23.2/Modules/UIElements/Core/Panel.cs:567)
UnityEngine.UIElements.UIElementsUtility:DoDispatch(BaseVisualElementPanel) (at /Users/kristinnbragi/gitrepo/23.2/Modules/UIElements/Core/UIElementsUtility.cs:498)
UnityEngine.UIElements.UIElementsUtility:UnityEngine.UIElements.IUIElementsUtility.ProcessEvent(Int32, IntPtr, Boolean&) (at /Users/kristinnbragi/gitrepo/23.2/Modules/UIElements/Core/UIElementsUtility.cs:225)
UnityEngine.UIElements.UIEventRegistration:ProcessEvent(Int32, IntPtr) (at /Users/kristinnbragi/gitrepo/23.2/Modules/UIElements/Core/UIElementsUtility.cs:74)
UnityEngine.UIElements.<>c:<.cctor>b__1_2(Int32, IntPtr) (at /Users/kristinnbragi/gitrepo/23.2/Modules/UIElements/Core/UIElementsUtility.cs:28)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr, Boolean&) (at /Users/kristinnbragi/gitrepo/23.2/Modules/IMGUI/GUIUtility.cs:206){code}