Fixed some sonar-reported issues.
diff --git a/net/api/src/main/java/org/onlab/onos/event/AbstractListenerRegistry.java b/net/api/src/main/java/org/onlab/onos/event/AbstractListenerRegistry.java
index 5e6011a..9710306 100644
--- a/net/api/src/main/java/org/onlab/onos/event/AbstractListenerRegistry.java
+++ b/net/api/src/main/java/org/onlab/onos/event/AbstractListenerRegistry.java
@@ -45,7 +45,7 @@
         for (L listener : listeners) {
             try {
                 listener.event(event);
-            } catch (Throwable error) {
+            } catch (Exception error) {
                 reportProblem(event, error);
             }
         }