Maximizing track from inspector throws null reference exception and maximized window shows no data.

Steps to Repro:
1. Create a new Project
2. Hierarchy > Right click > Cube.
3. Window > Sequencing > Timeline.
4. Create and save the timeline for Cube.
5. Select Cube timeline in the timeline window.
6. Inspector > Burger menu > Maximize

Actual Result:
NullReferenceException occurs window appears blank.

Expected Result:
Animation Track gets maximized gracefully with all parameters.

Environment:
Windows and Mac

Occurring with:
2019.3.0a4, 2019.2.0b4, 2019.2.0a6

Working with:
2019.2.0a5, 2019.1.0f2

Note:
The maximized track window appears blank from unity 2018.1.0f2

Stack Trace:
1. NullReferenceException: Object reference not set to an instance of an object
UnityEditor.Timeline.TrackAssetInspector.<IsTrackLocked>b__7_0 (UnityEngine.Object track) (at /Applications/Unity 2019.3.0a4/Unity.app/Contents/Resources/PackageManager/BuiltInPackages/com.unity.timeline/Editor/inspectors/TrackAssetInspector.cs:58)
System.Linq.Enumerable.Any[TSource] (System.Collections.Generic.IEnumerable`1[T] source, System.Func`2[T,TResult] predicate) (at <b7efe7e6e548497fac3c4a6049a0a4b6>:0)
UnityEditor.Timeline.TrackAssetInspector.IsTrackLocked () (at /Applications/Unity 2019.3.0a4/Unity.app/Contents/Resources/PackageManager/BuiltInPackages/com.unity.timeline/Editor/inspectors/TrackAssetInspector.cs:58)
UnityEditor.Timeline.TrackAssetInspector.DrawHeaderHelpAndSettingsGUI (UnityEngine.Rect r) (at /Applications/Unity 2019.3.0a4/Unity.app/Contents/Resources/PackageManager/BuiltInPackages/com.unity.timeline/Editor/inspectors/TrackAssetInspector.cs:122)
UnityEditor.Editor.DrawHeaderGUI (UnityEditor.Editor editor, System.String header, System.Single leftMargin) (at /Users/builduser/buildslave/unity/build/Editor/Mono/Inspector/Editor.cs:893)
UnityEditor.Editor.DrawHeaderGUI (UnityEditor.Editor editor, System.String header) (at /Users/builduser/buildslave/unity/build/Editor/Mono/Inspector/Editor.cs:854)
UnityEditor.Editor.OnHeaderGUI () (at /Users/builduser/buildslave/unity/build/Editor/Mono/Inspector/Editor.cs:747)
UnityEditor.Editor.DrawHeader () (at /Users/builduser/buildslave/unity/build/Editor/Mono/Inspector/Editor.cs:706)
UnityEditor.UIElements.EditorElement.DrawEditorLargeHeader (System.Boolean& wasVisible) (at /Users/builduser/buildslave/unity/build/Editor/Mono/Inspector/EditorElement.cs:305)
UnityEditor.UIElements.EditorElement.DrawEditorHeader (UnityEngine.Object target, System.Boolean& wasVisible) (at /Users/builduser/buildslave/unity/build/Editor/Mono/Inspector/EditorElement.cs:266)
UnityEditor.UIElements.EditorElement.HeaderOnGUI () (at /Users/builduser/buildslave/unity/build/Editor/Mono/Inspector/EditorElement.cs:212)
UnityEngine.UIElements.IMGUIContainer.DoOnGUI (UnityEngine.Event evt, UnityEngine.Matrix4x4 parentTransform, UnityEngine.Rect clippingRect, System.Boolean isComputingLayout, UnityEngine.Rect layoutSize) (at /Users/builduser/buildslave/unity/build/Modules/UIElements/IMGUIContainer.cs:280)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)

2. NullReferenceException: Object reference not set to an instance of an object
UnityEditor.Timeline.TrackAssetInspector.IsEnabled () (at /Applications/Unity 2019.3.0a4/Unity.app/Contents/Resources/PackageManager/BuiltInPackages/com.unity.timeline/Editor/inspectors/TrackAssetInspector.cs:71)
UnityEditor.UIElements.InspectorElement+<CreateIMGUIInspectorFromEditor>c__AnonStorey1.<>m__0 () (at /Users/builduser/buildslave/unity/build/Editor/Mono/Inspector/InspectorElement.cs:426)
UnityEngine.UIElements.IMGUIContainer.DoOnGUI (UnityEngine.Event evt, UnityEngine.Matrix4x4 parentTransform, UnityEngine.Rect clippingRect, System.Boolean isComputingLayout, UnityEngine.Rect layoutSize) (at /Users/builduser/buildslave/unity/build/Modules/UIElements/IMGUIContainer.cs:280)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)

3. NullReferenceException: Object reference not set to an instance of an object
UnityEngine.UIElements.UIR.RenderChain.Render (UnityEngine.Rect topRect, UnityEngine.Matrix4x4 projection) (at /Users/builduser/buildslave/unity/build/Modules/UIElements/Renderer/UIRChainBuilder.cs:236)
UnityEngine.UIElements.UIRRepaintUpdater.DrawChain (UnityEngine.Rect topRect, UnityEngine.Matrix4x4 projection) (at /Users/builduser/buildslave/unity/build/Modules/UIElements/Renderer/UIRRepaintUpdater.cs:60)
UnityEngine.UIElements.UIRRepaintUpdater.Update () (at /Users/builduser/buildslave/unity/build/Modules/UIElements/Renderer/UIRRepaintUpdater.cs:48)
UnityEngine.UIElements.VisualTreeUpdater.UpdateVisualTree () (at /Users/builduser/buildslave/unity/build/Modules/UIElements/VisualTreeUpdater.cs:73)
UnityEngine.UIElements.Panel.Repaint (UnityEngine.Event e) (at /Users/builduser/buildslave/unity/build/Modules/UIElements/Panel.cs:689)
UnityEngine.UIElements.UIElementsUtility.DoDispatch (UnityEngine.UIElements.BaseVisualElementPanel panel) (at /Users/builduser/buildslave/unity/build/Modules/UIElements/UIElementsUtility.cs:274)
UnityEngine.UIElements.UIElementsUtility.ProcessEvent (System.Int32 instanceID, System.IntPtr nativeEventPtr) (at /Users/builduser/buildslave/unity/build/Modules/UIElements/UIElementsUtility.cs:107)
UnityEngine.GUIUtility.ProcessEvent (System.Int32 instanceID, System.IntPtr nativeEventPtr) (at /Users/builduser/buildslave/unity/build/Modules/IMGUI/GUIUtility.cs:179)