Fix for ONOS-5152:Encoder for Disjoint Rest API with NPE:onos-1.7

Change-Id: I172e247353f7d70f6d7761e8a6be27f21b3c2684
diff --git a/core/api/src/main/java/org/onosproject/net/DefaultDisjointPath.java b/core/api/src/main/java/org/onosproject/net/DefaultDisjointPath.java
index 1f549a6..c4e0398 100644
--- a/core/api/src/main/java/org/onosproject/net/DefaultDisjointPath.java
+++ b/core/api/src/main/java/org/onosproject/net/DefaultDisjointPath.java
@@ -45,6 +45,16 @@
         this.path2 = path2;
     }
 
+    /**
+     * Creates a disjoint path pair from single default paths.
+     *
+     * @param providerId provider identity
+     * @param path1      primary path
+     */
+    public DefaultDisjointPath(ProviderId providerId, DefaultPath path1) {
+        this(providerId, path1, null);
+    }
+
     @Override
     public List<Link> links() {
         if (usingPath1) {