null reference error on adding actions with no action maps fix (#1703)

Author: ritamerkl

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

@@ -85,7 +85,7 @@ public static Command DeleteActionMap(int actionMapIndex)
 
         private static InputActionsEditorState SelectPrevActionMap(InputActionsEditorState state)
         {
-            var count = Selectors.GetActionMapCount(state.serializedObject);
+            var count = Selectors.GetActionMapCount(state);
             int index = -1;
             if (count != null && count.Value > 0)
                 index = Math.Max(state.selectedActionMapIndex - 1, 0);

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

@@ -112,13 +112,14 @@ public ActionsTreeView(VisualElement root, StateContainer stateContainer)
 
             m_ActionsTreeView.RegisterCallback<KeyDownEvent>(OnKeyDownEvent);
 
-            CreateSelector(Selectors.GetActionsForSelectedActionMap,
-                (_, state) =>
+            CreateSelector(Selectors.GetActionsForSelectedActionMap, Selectors.GetActionMapCount,
+                (_, count, state) =>
                 {
                     var treeData = Selectors.GetActionsAsTreeViewData(state);
                     return new ViewState
                     {
                         treeViewData = treeData,
+                        actionMapCount = count ?? 0,
                         newElementID = GetSelectedElementId(state, treeData)
                     };
                 });
@@ -174,6 +175,7 @@ public override void RedrawUI(ViewState viewState)
             if (viewState.newElementID != -1)
                 m_ActionsTreeView.SetSelectionById(viewState.newElementID);
             RenameNewAction(viewState.newElementID);
+            addActionButton.SetEnabled(viewState.actionMapCount > 0);
         }
 
         private void RenameNewAction(int id)
@@ -242,6 +244,7 @@ private void OnKeyDownEventForDelete()
         internal class ViewState
         {
             public List<TreeViewItemData<ActionOrBindingData>> treeViewData;
+            public int actionMapCount;
             public int newElementID;
         }
     }

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

@@ -56,9 +56,9 @@ public static IEnumerable<SerializedInputAction> GetActionsForSelectedActionMap(
             return actionMap?.FindPropertyRelative(nameof(InputActionMap.m_Actions))?.arraySize;
         }
 
-        public static int? GetActionMapCount(SerializedObject serializedObject)
+        public static int? GetActionMapCount(InputActionsEditorState state)
         {
-            return serializedObject?.FindProperty(nameof(InputActionAsset.m_ActionMaps))?.arraySize;
+            return state.serializedObject?.FindProperty(nameof(InputActionAsset.m_ActionMaps))?.arraySize;
         }
 
         public static SerializedInputAction GetActionInMap(InputActionsEditorState state, int mapIndex, string name)