Check for dangling action references in Inspector and set them to "None"

A dangling action reference means a actin reference that point to a non-existent InputAction.
This needs to be checked here in case an input action is removed from the project-wide actions asset. Otherwise the UI will still hold on to a dangling action reference.

Author: jfreire-unity

Packages/com.unity.inputsystem/InputSystem/Editor/PropertyDrawers/InputActionReferencePropertyDrawer.cs

@@ -15,16 +15,32 @@ internal sealed class InputActionReferencePropertyDrawer : PropertyDrawer
     {
         private readonly SearchContext m_Context = UnityEditor.Search.SearchService.CreateContext(new[]
         {
-            AssetSearchProviders.CreateInputActionReferenceSearchProviderForAssets(),
-            AssetSearchProviders.CreateInputActionReferenceSearchProviderForProjectWideActions(),
+            InputActionReferenceSearchProviders.CreateInputActionReferenceSearchProviderForAssets(),
+            InputActionReferenceSearchProviders.CreateInputActionReferenceSearchProviderForProjectWideActions(),
         }, string.Empty, SearchConstants.PickerSearchFlags);
 
 
         public override void OnGUI(Rect position, SerializedProperty property, GUIContent label)
         {
+            // Sets the property to null if the action is not found in the asset.
+            ValidatePropertyWithDanglingInputActionReferences(property);
+
             ObjectField.DoObjectField(position, property, typeof(InputActionReference), label,
                 m_Context, SearchConstants.PickerViewFlags);
         }
+
+        static void ValidatePropertyWithDanglingInputActionReferences(SerializedProperty property)
+        {
+            if (property?.objectReferenceValue is InputActionReference reference)
+            {
+                var action = reference?.asset?.FindAction(reference.action.id);
+                if (action is null)
+                {
+                    property.objectReferenceValue = null;
+                    property.serializedObject.ApplyModifiedProperties();
+                }
+            }
+        }
     }
 }
 

Packages/com.unity.inputsystem/InputSystem/Editor/UITKAssetEditor/InputActionsEditorSettingsProvider.cs

@@ -35,7 +35,7 @@ public override void OnActivate(string searchContext, VisualElement rootElement)
             // Note that focused element will be set if we are navigating back to
             // an existing instance when switching setting in the left project settings panel since
             // this doesn't recreate the editor.
-            if (m_RootVisualElement.focusController.focusedElement != null)
+            if (m_RootVisualElement?.focusController?.focusedElement != null)
                 OnEditFocus(null);
         }