Fixed InputActionDrawerBase not initializing the TreeView correctly to fix NullReferenceException when using Prefab Overrides window

[chris-massie]

Description

This PR addresses a bug where the Prefab Overrides dropdown window would trigger a NullReferenceException when drawing a component that has an InputActionProperty with a singleton action (i.e. Use Reference unchecked).

Changes made

• This change makes sure the TreeView.serializedObject matches the property. The value was null which was causing OnGUI to throw an exception.
• The change to UpdateSerializedObjectDirtyCount was not necessary for this fix but it should protect against cases where the serializedObject becomes null for some unknown reason. The EditorUtility.GetDirtyCount method returns 0 when the argument is null, so this seems like the appropriate thing to do.

Notes

This was causing exceptions when looking at overrides of XRI components.

ArgumentNullException: Value cannot be null.
Parameter name: _unity_self
UnityEngine.InputSystem.Editor.InputActionTreeView.UpdateSerializedObjectDirtyCount () (at Library/PackageCache/com.unity.inputsystem@1.3.0/InputSystem/Editor/AssetEditor/InputActionTreeView.cs:1394)
UnityEngine.InputSystem.Editor.InputActionTreeView.ReloadIfSerializedObjectHasBeenChanged () (at Library/PackageCache/com.unity.inputsystem@1.3.0/InputSystem/Editor/AssetEditor/InputActionTreeView.cs:1400)
UnityEngine.InputSystem.Editor.InputActionTreeView.OnGUI (UnityEngine.Rect rect) (at Library/PackageCache/com.unity.inputsystem@1.3.0/InputSystem/Editor/AssetEditor/InputActionTreeView.cs:1173)
UnityEngine.InputSystem.Editor.InputActionDrawerBase.OnGUI (UnityEngine.Rect position, UnityEditor.SerializedProperty property, UnityEngine.GUIContent label) (at Library/PackageCache/com.unity.inputsystem@1.3.0/InputSystem/Editor/PropertyDrawers/InputActionDrawerBase.cs:31)
UnityEditor.PropertyDrawer.OnGUISafe (UnityEngine.Rect position, UnityEditor.SerializedProperty property, UnityEngine.GUIContent label) (at <a5bc71bb4d98498aba1f868b89d20d47>:0)
UnityEditor.PropertyHandler.OnGUI (UnityEngine.Rect position, UnityEditor.SerializedProperty property, UnityEngine.GUIContent label, System.Boolean includeChildren, UnityEngine.Rect visibleArea) (at <a5bc71bb4d98498aba1f868b89d20d47>:0)
UnityEditor.PropertyHandler.OnGUI (UnityEngine.Rect position, UnityEditor.SerializedProperty property, UnityEngine.GUIContent label, System.Boolean includeChildren) (at <a5bc71bb4d98498aba1f868b89d20d47>:0)
UnityEditor.EditorGUI.PropertyFieldInternal (UnityEngine.Rect position, UnityEditor.SerializedProperty property, UnityEngine.GUIContent label, System.Boolean includeChildren) (at <a5bc71bb4d98498aba1f868b89d20d47>:0)
UnityEditor.EditorGUI.PropertyField (UnityEngine.Rect position, UnityEditor.SerializedProperty property, System.Boolean includeChildren) (at <a5bc71bb4d98498aba1f868b89d20d47>:0)
UnityEditor.EditorGUI.PropertyField (UnityEngine.Rect position, UnityEditor.SerializedProperty property) (at <a5bc71bb4d98498aba1f868b89d20d47>:0)
UnityEngine.InputSystem.Editor.InputActionPropertyDrawer.OnGUI (UnityEngine.Rect position, UnityEditor.SerializedProperty property, UnityEngine.GUIContent label) (at Library/PackageCache/com.unity.inputsystem@1.3.0/InputSystem/Editor/PropertyDrawers/InputActionPropertyDrawer.cs:77)
UnityEditor.PropertyDrawer.OnGUISafe (UnityEngine.Rect position, UnityEditor.SerializedProperty property, UnityEngine.GUIContent label) (at <a5bc71bb4d98498aba1f868b89d20d47>:0)
UnityEditor.PropertyHandler.OnGUI (UnityEngine.Rect position, UnityEditor.SerializedProperty property, UnityEngine.GUIContent label, System.Boolean includeChildren, UnityEngine.Rect visibleArea) (at <a5bc71bb4d98498aba1f868b89d20d47>:0)
UnityEditor.PropertyHandler.OnGUI (UnityEngine.Rect position, UnityEditor.SerializedProperty property, UnityEngine.GUIContent label, System.Boolean includeChildren) (at <a5bc71bb4d98498aba1f868b89d20d47>:0)
UnityEditor.PropertyHandler.OnGUILayout (UnityEditor.SerializedProperty property, UnityEngine.GUIContent label, System.Boolean includeChildren, UnityEngine.GUILayoutOption[] options) (at <a5bc71bb4d98498aba1f868b89d20d47>:0)
UnityEditor.EditorGUILayout.PropertyField (UnityEditor.SerializedProperty property, UnityEngine.GUIContent label, System.Boolean includeChildren, UnityEngine.GUILayoutOption[] options) (at <a5bc71bb4d98498aba1f868b89d20d47>:0)
UnityEditor.EditorGUILayout.PropertyField (UnityEditor.SerializedProperty property, UnityEngine.GUIContent label, UnityEngine.GUILayoutOption[] options) (at <a5bc71bb4d98498aba1f868b89d20d47>:0)
UnityEditor.XR.Interaction.Toolkit.ActionBasedControllerEditor.DrawTrackingConfiguration () (at C:/UnitySrc/com.unity.xr.interaction.toolkit-2.1/com.unity.xr.interaction.toolkit/Editor/Interaction/Controllers/ActionBasedControllerEditor.cs:93)
UnityEditor.XR.Interaction.Toolkit.XRBaseControllerEditor.DrawProperties () (at C:/UnitySrc/com.unity.xr.interaction.toolkit-2.1/com.unity.xr.interaction.toolkit/Editor/Interaction/Controllers/XRBaseControllerEditor.cs:135)
UnityEditor.XR.Interaction.Toolkit.XRBaseControllerEditor.DrawInspector () (at C:/UnitySrc/com.unity.xr.interaction.toolkit-2.1/com.unity.xr.interaction.toolkit/Editor/Interaction/Controllers/XRBaseControllerEditor.cs:112)
UnityEditor.XR.Interaction.Toolkit.BaseInteractionEditor.OnInspectorGUI () (at C:/UnitySrc/com.unity.xr.interaction.toolkit-2.1/com.unity.xr.interaction.toolkit/Editor/BaseInteractionEditor.cs:28)
UnityEditor.PrefabOverridesTreeView+ComparisonViewPopup.DrawEditor (UnityEngine.Rect rect, UnityEditor.Editor editor, System.Boolean disabled) (at <a5bc71bb4d98498aba1f868b89d20d47>:0)
UnityEditor.PrefabOverridesTreeView+ComparisonViewPopup.OnGUI (UnityEngine.Rect rect) (at <a5bc71bb4d98498aba1f868b89d20d47>:0)
UnityEditor.PopupWindow.OnGUI () (at <a5bc71bb4d98498aba1f868b89d20d47>:0)
UnityEditor.HostView.OldOnGUI () (at <a5bc71bb4d98498aba1f868b89d20d47>:0)
UnityEngine.UIElements.IMGUIContainer.DoOnGUI (UnityEngine.Event evt, UnityEngine.Matrix4x4 parentTransform, UnityEngine.Rect clippingRect, System.Boolean isComputingLayout, UnityEngine.Rect layoutSize, System.Action onGUIHandler, System.Boolean canAffectFocus) (at <c735460d95a241ccbea413909634f410>:0)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr, Boolean&)

Checklist

Before review:

• Changelog entry added.
  • Explains the change in Changed, Fixed, Added sections.
  • For API change contains an example snippet and/or migration example.
  • FogBugz ticket attached, example ([case %number%](https://issuetracker.unity3d.com/issues/...)).
  • FogBugz is marked as "Resolved" with next release version correctly set.
• Tests added/changed, if applicable.
  • Functional tests Area_CanDoX, Area_CanDoX_EvenIfYIsTheCase, Area_WhenIDoX_AndYHappens_ThisIsTheResult.
  • Performance tests.
  • Integration tests.
• Docs for new/changed API's.
  • Xmldoc cross references are set correctly.
  • Added explanation how the API works.
  • Usage code examples added.
  • The manual is updated, if needed.

During merge:

• Commit message for squash-merge is prefixed with one of the list:
  • NEW: ___.
  • FIX: ___.
  • DOCS: ___.
  • CHANGE: ___.
  • RELEASE: 1.1.0-preview.3.

[ekcoh]

@chris-massie I updated the changelog conflict and can merge this one as soon as CI is green.

[chris-massie]

@ekcoh I updated the changelog conflict again and the CI tests are all passing. This is ready to merge.

[andrew-oc]

Shouldn't this should be under the [Unreleased] section?

[jamesmcgill]

I'm in the middle of the release just now, so develop doesn't have the [Unreleased] section right now. That's probably why it's went here.
I will move this into [Unreleased] after I put it back and bump to v1.4.4 for the next release.

[jamesmcgill]

Thanks for the PR @chris-massie !