Potential NPE in DeleteService.collectRelatedElements()

[pcdavid]

I don't know what's special with this model (could not reproduce in a fresh project), but I have a case where an element (a ConnectionDefinition) can not be deleted from the Explorer, with no error message:

In the backend's log I see this stack:

Caused by: java.lang.NullPointerException: Cannot invoke "java.util.Set.iterator()" because "collectedElements" is null
	at org.eclipse.syson.services.DeleteService.collectRelatedElements(DeleteService.java:67) ~[syson-services-2025.12.5.jar!/:2025.12.5]
	at org.eclipse.syson.services.DeleteService.collectRelatedElements(DeleteService.java:70) ~[syson-services-2025.12.5.jar!/:2025.12.5]
	at org.eclipse.syson.services.DeleteService.lambda$deleteFromModel$0(DeleteService.java:54) ~[syson-services-2025.12.5.jar!/:2025.12.5]
	at java.base/java.util.Iterator.forEachRemaining(Unknown Source) ~[na:na]
	at org.eclipse.syson.services.DeleteService.deleteFromModel(DeleteService.java:54) ~[syson-services-2025.12.5.jar!/:2025.12.5]
	at org.eclipse.syson.application.services.SysMLv2EditService.lambda$delete$4(SysMLv2EditService.java:295) ~[syson-application-configuration-2025.12.5.jar!/:2025.12.5]
	at java.base/java.util.Optional.ifPresent(Unknown Source) ~[na:na]
	at org.eclipse.syson.application.services.SysMLv2EditService.delete(SysMLv2EditService.java:295) ~[syson-application-configuration-2025.12.5.jar!/:2025.12.5]
	at org.eclipse.sirius.components.core.services.ComposedEditService.lambda$delete$5(ComposedEditService.java:94) ~[sirius-components-core-2025.12.5.jar!/:2025.12.5]
	at java.base/java.util.Optional.ifPresentOrElse(Unknown Source) ~[na:na]
	at org.eclipse.sirius.components.core.services.ComposedEditService.delete(ComposedEditService.java:94) ~[sirius-components-core-2025.12.5.jar!/:2025.12.5]
	at org.eclipse.sirius.web.application.views.explorer.services.DeleteObjectTreeItemEventHandler.handle(DeleteObjectTreeItemEventHandler.java:73) ~[sirius-web-application-2025.12.5.jar!/:2025.12.5]