diff --git a/src/main/java/net/onrc/onos/ofcontroller/networkgraph/AbstractNetworkGraph.java b/src/main/java/net/onrc/onos/ofcontroller/networkgraph/AbstractNetworkGraph.java
index d84de5f..b2f9247 100644
--- a/src/main/java/net/onrc/onos/ofcontroller/networkgraph/AbstractNetworkGraph.java
+++ b/src/main/java/net/onrc/onos/ofcontroller/networkgraph/AbstractNetworkGraph.java
@@ -97,7 +97,7 @@
 	public Iterable<Device> getDeviceByIp(InetAddress ipAddress) {
 		Set<Device> devices = addr2Device.get(ipAddress);
 		if (devices == null) {
-			return Collections.emptyList();
+			return Collections.emptySet();
 		}
 		return Collections.unmodifiableCollection(devices);
 	}
diff --git a/src/main/java/net/onrc/onos/ofcontroller/networkgraph/Device.java b/src/main/java/net/onrc/onos/ofcontroller/networkgraph/Device.java
index e25e812..cd5ddf8 100644
--- a/src/main/java/net/onrc/onos/ofcontroller/networkgraph/Device.java
+++ b/src/main/java/net/onrc/onos/ofcontroller/networkgraph/Device.java
@@ -8,6 +8,8 @@
 /**
  * Interface of Device Object exposed to the "NB" read-only Topology.
  *
+ * TODO What a Device Object represent is unclear at the moment.
+ *
  * Everything returned by these interfaces must be either Unmodifiable view,
  * immutable object, or a copy of the original "SB" In-memory Topology.
  *
@@ -17,6 +19,7 @@
 
 	public Collection<InetAddress> getIpAddress();
 
+	// Add requirement for Iteration order? Latest observed port first.
 	public Iterable<Port> getAttachmentPoints();
 
 	public long getLastSeenTime();