FIX: ISXB-1081 Fixed "MissingReferenceException" errors when closing an in-game dropdown field (#2010)

Author: bmalrat

Packages/com.unity.inputsystem/CHANGELOG.md

@@ -14,6 +14,7 @@ however, it has to be formatted properly to pass verification tests.
 - Fixed Multiple interactions could breaks on Composite Binding. [ISXB-619](https://issuetracker.unity3d.com/product/unity/issues/guid/ISXB-619)
 - Fixed memory leak when the OnScreenStick component was destroyed [ISXB-1070](https://issuetracker.unity3d.com/product/unity/issues/guid/ISXB-1070). Contribution by [LukeUnityDev](https://github.com/LukeUnityDev).
 - Fixed Action Maps contextual menu in Action Editor UI that occasionally displays unrelated items.
+- Fixed "MissingReferenceException" errors when closing an in-game dropdown field [ISXB-1081](https://issuetracker.unity3d.com/product/unity/issues/guid/ISXB-1081).
 
 ### Changed
 - Renamed editor Resources directories to PackageResources to fix package validation warnings.

Packages/com.unity.inputsystem/InputSystem/Plugins/UI/InputSystemUIInputModule.cs

@@ -473,7 +473,7 @@ private void ProcessPointerMovement(ExtendedPointerEventData eventData, GameObje
             }
 
             // now issue the enter call up to but not including the common root
-            Transform oldPointerEnter = eventData.pointerEnter?.transform;
+            Transform oldPointerEnter = eventData.pointerEnter ? eventData.pointerEnter.transform : null;
             eventData.pointerEnter = currentPointerTarget;
             if (currentPointerTarget != null)
             {