Renamed AbstractListenerRegistry to ListenerRegistry (since it is not abstract).
- added checkForNonRegistrant() predicate and augmented unit tests.

Change-Id: I7ecc618f01fdc4cead6f143a1e5e0ddd03268efc
diff --git a/web/gui/src/main/java/org/onosproject/ui/impl/topo/ModelListenerRegistry.java b/web/gui/src/main/java/org/onosproject/ui/impl/topo/ModelListenerRegistry.java
index 04c6b72..eacbbaf 100644
--- a/web/gui/src/main/java/org/onosproject/ui/impl/topo/ModelListenerRegistry.java
+++ b/web/gui/src/main/java/org/onosproject/ui/impl/topo/ModelListenerRegistry.java
@@ -17,7 +17,7 @@
 
 package org.onosproject.ui.impl.topo;
 
-import org.onosproject.event.AbstractListenerRegistry;
+import org.onosproject.event.ListenerRegistry;
 import org.slf4j.Logger;
 
 import java.util.HashSet;
@@ -31,7 +31,7 @@
  */
 // package private
 class ModelListenerRegistry
-        extends AbstractListenerRegistry<TopoUiEvent, TopoUiListener> {
+        extends ListenerRegistry<TopoUiEvent, TopoUiListener> {
 
     private final Logger log = getLogger(getClass());
 
@@ -58,4 +58,9 @@
             removeListener(z);
         }
     }
+
+    @Override
+    protected boolean checkForNonRegistrant() {
+        return false;
+    }
 }
diff --git a/web/gui/src/main/java/org/onosproject/ui/impl/topo/TopoUiModelManager.java b/web/gui/src/main/java/org/onosproject/ui/impl/topo/TopoUiModelManager.java
index c80c2e2..3c355ab 100644
--- a/web/gui/src/main/java/org/onosproject/ui/impl/topo/TopoUiModelManager.java
+++ b/web/gui/src/main/java/org/onosproject/ui/impl/topo/TopoUiModelManager.java
@@ -143,12 +143,7 @@
 
     @Override
     public void removeListener(TopoUiListener listener) {
-        // we don't really care if the listener is not listed...
-        try {
-            listenerRegistry.removeListener(listener);
-        } catch (IllegalArgumentException e) {
-            log.debug("Oops, listener not registered: {}", listener);
-        }
+        listenerRegistry.removeListener(listener);
     }
 
     @Override