FIX: Parameter-less processors and interactions show a plain header instead of an empty foldout in the Input Actions editor [UUM-144325]

In the UITK Input Actions editor's Action Properties view, every processor/interaction list item was rendered with an expandable foldout regardless of whether it had any editable parameters, so a parameter-less processor such as "Invert" showed a foldout whose arrow animated on click but revealed no content.

The NameAndParametersListViewItem(VisualElement root, ParameterListView parameterListView, ButtonProperties buttonProperties) constructor now gates the foldout content on parameterListView.hasUIToShow. When there are no editable parameters it hides the header toggle's expand arrow (unity-toggle__checkmark) and sets the toggle's pickingMode to Ignore, so the item reads as a plain, non-collapsible header while the move-up/move-down/delete buttons stay clickable. This mirrors the IMGUI editor, which uses the same hasUIToShow predicate to choose foldout-vs-label.

Jira: https://jira.unity3d.com/browse/UUM-144325

Author: Pauliusd01

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 parameter-less processors and interactions (e.g. "Invert") in the Input Actions editor's Action Properties view showing an expandable foldout whose arrow animated on click but revealed no content; such items are now rendered as a plain, non-collapsible header [UUM-144325](https://issuetracker.unity3d.com/product/unity/issues/guid/UUM-144325)
 - Fixed the Input Debugger window (Window > Analysis > Input Debugger) being resizable arbitrarily small until its toolbar and device/action/layout tree view were no longer usably visible; it now enforces a minimum window size [UUM-137119](https://issuetracker.unity3d.com/product/unity/issues/guid/UUM-137119)
 - Fixed the Action Maps list in the Input Actions editor losing keyboard focus after deleting a map, so that Delete, Duplicate, and arrow-key navigation kept working on the auto-selected replacement map without requiring an extra click [UUM-147152](https://issuetracker.unity3d.com/product/unity/issues/guid/UUM-147152)
 

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

@@ -170,9 +170,24 @@ public NameAndParametersListViewItem(VisualElement root, ParameterListView param
 
             var foldout = container.Q<Foldout>("Foldout");
             foldout.text = parameterListView.name;
-            parameterListView.OnDrawVisualElements(foldout);
 
-            foldout.Add(new IMGUIContainer(parameterListView.OnGUI));
+            // A parameter-less processor/interaction (e.g. "Invert") has no content to reveal, so render it as
+            // a plain, non-collapsible header rather than an empty foldout whose arrow animates but shows nothing.
+            // Mirrors the IMGUI editor, which uses the same hasUIToShow predicate to choose foldout-vs-label.
+            if (parameterListView.hasUIToShow)
+            {
+                parameterListView.OnDrawVisualElements(foldout);
+                foldout.Add(new IMGUIContainer(parameterListView.OnGUI));
+            }
+            else
+            {
+                // Hide the expand arrow and disable picking on the header toggle; the move/delete buttons are
+                // separate child elements and remain clickable.
+                var checkmark = header.Q(className: "unity-toggle__checkmark");
+                if (checkmark != null)
+                    checkmark.style.display = DisplayStyle.None;
+                header.pickingMode = PickingMode.Ignore;
+            }
         }
     }
 }