Created onos-core-trivial as a place to put trivial implementation of core against which initial set of providers can be developed.
diff --git a/net/api/src/main/java/org/onlab/onos/net/provider/AbstractProviderBroker.java b/net/api/src/main/java/org/onlab/onos/net/provider/AbstractProviderBroker.java
index a783fec..ad1e0ab 100644
--- a/net/api/src/main/java/org/onlab/onos/net/provider/AbstractProviderBroker.java
+++ b/net/api/src/main/java/org/onlab/onos/net/provider/AbstractProviderBroker.java
@@ -38,10 +38,9 @@
     public synchronized void unregister(P provider) {
         checkNotNull(provider, "Provider cannot be null");
         S service = services.get(provider);
-        checkArgument(service != null, "Provider %s not registered", provider.id());
-        if (service instanceof AbstractProviderService) {
+        if (service != null && service instanceof AbstractProviderService) {
             ((AbstractProviderService) service).invalidate();
+            services.remove(provider);
         }
-        services.remove(provider);
     }
 }