Collections.emptyMap() produces an object that Kryo cannot serialize

Change-Id: I12c105ecbcff560a62e5e883f18c0e75dd69c078

@@ -16,21 +16,19 @@
 
 package org.onosproject.net.intent;
 
-import java.util.Collections;
-import java.util.List;
-import java.util.Map;
-import java.util.Set;
-
 import com.google.common.annotations.Beta;
+import com.google.common.base.MoreObjects;
 import com.google.common.collect.ImmutableMap;
+import com.google.common.collect.ImmutableSet;
 import org.onosproject.core.ApplicationId;
 import org.onosproject.net.ConnectPoint;
 import org.onosproject.net.Link;
 import org.onosproject.net.flow.TrafficSelector;
 import org.onosproject.net.flow.TrafficTreatment;
 
-import com.google.common.base.MoreObjects;
-import com.google.common.collect.ImmutableSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
 
 /**
  * Abstraction of a connectivity intent that is implemented by a set of path
@@ -118,7 +116,7 @@ public final class LinkCollectionIntent extends ConnectivityIntent {
         Set<Link> links;
         Set<ConnectPoint> ingressPoints;
         Set<ConnectPoint> egressPoints;
-        Map<ConnectPoint, TrafficSelector> ingressSelectors = Collections.emptyMap();
+        Map<ConnectPoint, TrafficSelector> ingressSelectors = ImmutableMap.of();
         boolean egressTreatmentFlag;
 
         private Builder() {

@@ -25,7 +25,6 @@ import org.onosproject.net.ConnectPoint;
 import org.onosproject.net.flow.TrafficSelector;
 import org.onosproject.net.flow.TrafficTreatment;
 
-import java.util.Collections;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
@@ -74,7 +73,7 @@ public final class MultiPointToSinglePointIntent extends ConnectivityIntent {
                                           int priority,
                                           Map<ConnectPoint, TrafficSelector> ingressSelectors
                                           ) {
-        super(appId, key, Collections.emptyList(), selector, treatment, constraints,
+        super(appId, key, ImmutableSet.of(), selector, treatment, constraints,
                 priority);
 
         checkNotNull(ingressPoints);
@@ -127,7 +126,7 @@ public final class MultiPointToSinglePointIntent extends ConnectivityIntent {
     public static final class Builder extends ConnectivityIntent.Builder {
         Set<ConnectPoint> ingressPoints;
         ConnectPoint egressPoint;
-        Map<ConnectPoint, TrafficSelector> ingressSelectors = Collections.emptyMap();
+        Map<ConnectPoint, TrafficSelector> ingressSelectors = ImmutableMap.of();
 
         private Builder() {
             // Hide constructor