"NullReferenceException" is thrown when resetting the Editor layout while the Entities Relationships tab is open

Steps to reproduce:

1. Create a new URP project
2. Enable "Use new Hierarchy window" property in Preferences window
3. From the Package Manager, install the Entities package (com.unity.entities)
4. Right-click in the Hierarchy and select "New Sub Scene" > "Empty Scene..." and save the Sub Scene
5. Open the Entities Hierarchy window (Window > Entities > Hierarchy)
6. Select the created Sub Scene and click "Close" in the Inspector
7. Select the child of the closed Sub Scene (for example, "Entity(25:5)")
8. In the Inspector, navigate to the "Relationships" tab
9. In the Editor toolbar, select Layout > Default (to reset Editor layout)
10. Observe the Console

Actual results: "NullReferenceException: Object reference not set to an instance of an object
Unity.Entities.Editor.RelationshipsTab.GatherMatchingQueries (Unity.Entities.EntityComponentStore* ecs, Unity.Entities.Entity entity," error is thrown

Expected results: No errors are thrown

Reproducible with versions: 6000.5.0a7, 6000.5.0b6, 6000.6.0a4

Not reproducible with versions: 6000.5.0a6

Tested on (OS): macOS 26.4

Notes:

• In newer versions, the issue also reproduces without opening the Entities Hierarchy window, since the entity hierarchy workflow is available from the regular Hierarchy and the window is deprecated. The steps above use the Entities Hierarchy window to showcase steps for bisection
• Error seems to have appeared after Entities Hierarchy was merged