Added commands to list paths.
Added protection against bad input on some command-lines.
diff --git a/cli/src/main/java/org/onlab/onos/cli/net/ClusterDevicesCommand.java b/cli/src/main/java/org/onlab/onos/cli/net/ClusterDevicesCommand.java
index d4d6d24..a6f3048 100644
--- a/cli/src/main/java/org/onlab/onos/cli/net/ClusterDevicesCommand.java
+++ b/cli/src/main/java/org/onlab/onos/cli/net/ClusterDevicesCommand.java
@@ -35,11 +35,16 @@
         int cid = Integer.parseInt(id);
         init();
         TopologyCluster cluster = service.getCluster(topology, clusterId(cid));
-        List<DeviceId> ids = Lists.newArrayList(service.getClusterDevices(topology, cluster));
-        Collections.sort(ids, ID_COMPARATOR);
-        for (DeviceId deviceId : ids) {
-            print("%s", deviceId);
+        if (cluster == null) {
+            error("No such cluster %s", cid);
+        } else {
+            List<DeviceId> ids = Lists.newArrayList(service.getClusterDevices(topology, cluster));
+            Collections.sort(ids, ID_COMPARATOR);
+            for (DeviceId deviceId : ids) {
+                print("%s", deviceId);
+            }
         }
+
         return null;
     }