FIX: Only dispatch when there is a valid selected item when removing all action maps (#2383)

Author: josepmariapujol-unity

Packages/com.unity.inputsystem/CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ### Fixed
 
+- Fixed a `NullReferenceException` thrown when removing all action maps [UUM-137116](https://jira.unity3d.com/browse/UUM-137116)
 - Simplified default setting messaging by consolidating repetitive messages into a single HelpBox.
 - Fixed a `NullPointerReferenceException` thrown in `InputManagerStateMonitors.FireStateChangeNotifications` logging by adding validation [UUM-136095].
 - Fixed auto-save not working for Input System actions in Project Settings when both the Project Settings and Input System Actions windows were open [UUM-134035](https://jira.unity3d.com/browse/UUM-134035)

Packages/com.unity.inputsystem/InputSystem/Editor/UITKAssetEditor/Views/ActionMapsView.cs

@@ -21,7 +21,8 @@ public ActionMapsView(VisualElement root, StateContainer stateContainer)
             m_ListViewSelectionChangeFilter = new CollectionViewSelectionChangeFilter(m_ListView);
             m_ListViewSelectionChangeFilter.selectedIndicesChanged += (selectedIndices) =>
             {
-                Dispatch(Commands.SelectActionMap(((ActionMapData)m_ListView.selectedItem).mapName));
+                if (m_ListView.selectedItem is ActionMapData mapData)
+                    Dispatch(Commands.SelectActionMap(mapData.mapName));
             };
 
             m_ListView.bindItem = (element, i) =>