don't proceed with registration when event bus is missing.
diff --git a/bundles/org.eclipse.equinox.p2.garbagecollector/src/org/eclipse/equinox/p2/garbagecollector/GCActivator.java b/bundles/org.eclipse.equinox.p2.garbagecollector/src/org/eclipse/equinox/p2/garbagecollector/GCActivator.java
index 0629d51..798c689 100644
--- a/bundles/org.eclipse.equinox.p2.garbagecollector/src/org/eclipse/equinox/p2/garbagecollector/GCActivator.java
+++ b/bundles/org.eclipse.equinox.p2.garbagecollector/src/org/eclipse/equinox/p2/garbagecollector/GCActivator.java
@@ -54,6 +54,7 @@
 		ProvisioningEventBus eventBus = (ProvisioningEventBus) getService(GCActivator.context, ProvisioningEventBus.class.getName());
 		if (eventBus == null) {
 			LogHelper.log(new Status(IStatus.ERROR, GCActivator.ID, Messages.Missing_bus));
+			return;
 		}
 		eventBus.addListener(busListener = new SynchronousProvisioningListener() {
 			//The GC is triggered when an uninstall event occured during a "transaction" and the transaction is committed.