Editor throws NullReferenceException when mouse is hovered and Shift + space is pressed over a blank area (Non-window area) above Hierarchy tab.

Steps to Reproduce:
1. Create a new Project.
2. Hover mouse over non-window area (blank space above Hierarchy tab )
3. Press Shift + Space

Actual Result:
Editor throws NullReferenceException

Expected Result:
Editor should not throw any error.

Reproducible on:
2018.3.0a9, 2018.3.0a3

Working on:
2018.3.0a2, 2018.2.0f2

Note: Editor is crashing on pressing Shift + Space on 2018.3.0a8
Refer attached video.

Environment:
Occurring on Both Windows and Mac

Error Details :
NullReferenceException: Object reference not set to an instance of an object
UnityEditor.WindowLayout.IsMaximized (UnityEditor.EditorWindow window) (at /Users/builduser/buildslave/unity/build/Editor/Mono/GUI/WindowLayout.cs:214)
UnityEditor.WindowLayout.MaximizeKeyHandler (UnityEditor.ShortcutManagement.ShortcutArguments args) (at /Users/builduser/buildslave/unity/build/Editor/Mono/GUI/WindowLayout.cs:355)
System.Reflection.MonoMethod.Invoke (System.Object obj, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at <3599980ea7e14b228ba6a6ea6c050a5d>:0)
Rethrow as TargetInvocationException: Exception has been thrown by the target of an invocation.
System.Reflection.MonoMethod.Invoke (System.Object obj, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at <3599980ea7e14b228ba6a6ea6c050a5d>:0)
System.Reflection.MethodBase.Invoke (System.Object obj, System.Object[] parameters) (at <3599980ea7e14b228ba6a6ea6c050a5d>:0)
UnityEditor.ShortcutManagement.ShortcutAttribute+<CreateShortcutEntry>c__AnonStorey0.<>m__1 (UnityEditor.ShortcutManagement.ShortcutArguments shortcutArgs) (at /Users/builduser/buildslave/unity/build/Modules/ShortcutManagerEditor/ShortcutAttribute.cs:60)
UnityEditor.ShortcutManagement.Trigger.HandleKeyEvent (UnityEngine.Event evt, UnityEditor.ShortcutManagement.IContextManager contextManager) (at /Users/builduser/buildslave/unity/build/Modules/ShortcutManagerEditor/Trigger.cs:90)
UnityEditor.ShortcutManagement.ShortcutController.HandleInTrigger (UnityEngine.Event evt, UnityEditor.ShortcutManagement.IContextManager contextManager) (at /Users/builduser/buildslave/unity/build/Modules/ShortcutManagerEditor/ShortcutController.cs:79)
UnityEditor.ShortcutManagement.ShortcutController.HandleKeyEvent (UnityEngine.Event evt) (at /Users/builduser/buildslave/unity/build/Modules/ShortcutManagerEditor/ShortcutController.cs:74)
UnityEditor.ShortcutManagement.ShortcutIntegration.EventHandler () (at /Users/builduser/buildslave/unity/build/Modules/ShortcutManagerEditor/ShortcutController.cs:21)
UnityEditor.EditorApplication.Internal_CallGlobalEventHandler () (at /Users/builduser/buildslave/unity/build/Editor/Mono/EditorApplication.cs:312)