Reproduction steps:
1. Create a new project
2. Window > Package Management > Package Manager > Universal Render Pipeline
3. Click on Samples tab and observe the Console

Actual result: “NullReferenceException: Object reference not set to an instance of an object” error is thrown
Expected result: No warnings or errors are thrown

Reproducible with: 6000.5.0a1
Not reproducible with: 2022.3.68f1, 6000.0.62f1, 6000.2.12f1, 6000.3.0b10, 6000.4.0a3, 6000.4.0a4

Reproduced on: Ubuntu 22.04, macOS Sequoia 15.4 (M4)

Note:

• Full error:

{code:java}
NullReferenceException: Object reference not set to an instance of an object
SampleDependencyImporter.RefreshSampleButtons () (at ./Library/PackageCache/com.unity.render-pipelines.core@2c539e7b378a/Editor/SampleDependencyImportSystem/SampleDependencyImporter.cs:118)
UnityEngine.UIElements.Clickable.Invoke (UnityEngine.UIElements.EventBase evt) (at /Users/bokken/build/output/unity/unity/Modules/UIElements/Core/Clickable.cs:289)
UnityEngine.UIElements.Clickable.ProcessUpEvent (UnityEngine.UIElements.EventBase evt, UnityEngine.Vector2 localPosition, System.Int32 pointerId) (at /Users/bokken/build/output/unity/unity/Modules/UIElements/Core/Clickable.cs:386)
UnityEngine.UIElements.Clickable.OnPointerUp (UnityEngine.UIElements.PointerUpEvent evt) (at /Users/bokken/build/output/unity/unity/Modules/UIElements/Core/Clickable.cs:253)
UnityEngine.UIElements.EventCallbackFunctor`1[TEventType].Invoke (UnityEngine.UIElements.EventBase evt) (at /Users/bokken/build/output/unity/unity/Modules/UIElements/Core/Events/EventCallback.cs:64)
UnityEngine.UIElements.EventCallbackRegistry+DynamicCallbackList.Invoke (UnityEngine.UIElements.EventBase evt, UnityEngine.UIElements.BaseVisualElementPanel panel, UnityEngine.UIElements.VisualElement target) (at /Users/bokken/build/output/unity/unity/Modules/UIElements/Core/Events/EventCallbackRegistry.cs:246)
UnityEngine.UIElements.EventDispatchUtilities.HandleEventAcrossPropagationPathWithCompatibilityEvent (UnityEngine.UIElements.EventBase evt, UnityEngine.UIElements.EventBase compatibilityEvt, UnityEngine.UIElements.BaseVisualElementPanel panel, UnityEngine.UIElements.VisualElement target, System.Boolean isCapturingTarget) (at /Users/bokken/build/output/unity/unity/Modules/UIElements/Core/Events/EventDispatchUtilities.cs:334)
UnityEngine.UIElements.EventDispatchUtilities.DispatchToCapturingElementOrElementUnderPointer (UnityEngine.UIElements.EventBase evt, UnityEngine.UIElements.BaseVisualElementPanel panel, System.Int32 pointerId, UnityEngine.Vector2 position) (at /Users/bokken/build/output/unity/unity/Modules/UIElements/Core/Events/EventDispatchUtilities.cs:566)
UnityEngine.UIElements.PointerUpEvent.Dispatch (UnityEngine.UIElements.BaseVisualElementPanel panel) (at /Users/bokken/build/output/unity/unity/Modules/UIElements/Core/Events/PointerEvents.cs:1652)
UnityEngine.UIElements.EventDispatcher.ProcessEvent (UnityEngine.UIElements.EventBase evt, UnityEngine.UIElements.BaseVisualElementPanel panel) (at /Users/bokken/build/output/unity/unity/Modules/UIElements/Core/EventDispatcher.cs:419)
UnityEngine.UIElements.EventDispatcher.Dispatch (UnityEngine.UIElements.EventBase evt, UnityEngine.UIElements.BaseVisualElementPanel panel, UnityEngine.UIElements.DispatchMode dispatchMode) (at /Users/bokken/build/output/unity/unity/Modules/UIElements/Core/EventDispatcher.cs:215)
UnityEngine.UIElements.BaseVisualElementPanel.SendEvent (UnityEngine.UIElements.EventBase e, UnityEngine.UIElements.DispatchMode dispatchMode) (at /Users/bokken/build/output/unity/unity/Modules/UIElements/Core/Panel.cs:678)
UnityEngine.UIElements.UIElementsUtility.DoDispatch (UnityEngine.UIElements.BaseVisualElementPanel panel) (at /Users/bokken/build/output/unity/unity/Modules/UIElements/Core/UIElementsUtility.cs:546)
UnityEngine.UIElements.UIElementsUtility.UnityEngine.UIElements.IUIElementsUtility.ProcessEvent (UnityEngine.EntityId entityId, System.IntPtr nativeEventPtr, System.Boolean& eventHandled) (at /Users/bokken/build/output/unity/unity/Modules/UIElements/Core/UIElementsUtility.cs:245)
UnityEngine.UIElements.UIEventRegistration.ProcessEvent (UnityEngine.EntityId entityId, System.IntPtr nativeEventPtr) (at /Users/bokken/build/output/unity/unity/Modules/UIElements/Core/UIElementsUtility.cs:79)
UnityEngine.UIElements.UIEventRegistration+<>c.<.cctor>b__1_2 (UnityEngine.EntityId i, System.IntPtr ptr) (at /Users/bokken/build/output/unity/unity/Modules/UIElements/Core/UIElementsUtility.cs:33)
UnityEngine.GUIUtility.ProcessEvent (UnityEngine.EntityId entityId, System.IntPtr nativeEventPtr, System.Boolean& result) (at /Users/bokken/build/output/unity/unity/Modules/IMGUI/GUIUtility.cs:227)
{code}

• Sometimes additional error is thrown:

{code:java}
[Package Manager Window] Package manager extension failed with error: System.NullReferenceException: Object reference not set to an instance of an object
  at SampleDependencyImporter.RefreshSampleButtons () [0x00103] in ./Library/PackageCache/com.unity.render-pipelines.core@2c539e7b378a/Editor/SampleDependencyImportSystem/SampleDependencyImporter.cs:118 
  at SampleDependencyImporter.UnityEditor.PackageManager.UI.IPackageManagerExtension.OnPackageSelectionChange (UnityEditor.PackageManager.PackageInfo packageInfo) [0x0004b] in ./Library/PackageCache/com.unity.render-pipelines.core@2c539e7b378a/Editor/SampleDependencyImportSystem/SampleDependencyImporter.cs:171 
  at UnityEditor.PackageManager.UI.Internal.PackageDetails+<>c__DisplayClass22_0.<RefreshExtensions>b__0 () [0x00014] in /Users/bokken/build/output/unity/unity/Modules/PackageManagerUI/Editor/UI/PackageDetails.cs:205 
  at UnityEditor.PackageManager.UI.PackageManagerExtensions.ExtensionCallback (System.Action action) [0x00000] in /Users/bokken/build/output/unity/unity/Modules/PackageManagerUI/Editor/UI/PackageManagerExtensions.cs:35 
UnityEngine.GUIUtility:ProcessEvent (UnityEngine.EntityId,intptr,bool&) (at /Users/bokken/build/output/unity/unity/Modules/IMGUI/GUIUtility.cs:227)
{code}