Added null check for empty ArrayNode object in DhcpRelayWebResource.java

Change-Id: Iace1230e73ca44a6a0591de9c3d843bbc96743f9
(cherry picked from commit 4ae2b6f047da2facbd8be06cf2b1971c1381ec8b)
diff --git a/apps/dhcprelay/web/src/main/java/org/onosproject/dhcprelay/rest/DhcpRelayWebResource.java b/apps/dhcprelay/web/src/main/java/org/onosproject/dhcprelay/rest/DhcpRelayWebResource.java
index d5e142a..bf19691 100644
--- a/apps/dhcprelay/web/src/main/java/org/onosproject/dhcprelay/rest/DhcpRelayWebResource.java
+++ b/apps/dhcprelay/web/src/main/java/org/onosproject/dhcprelay/rest/DhcpRelayWebResource.java
@@ -163,9 +163,15 @@
      */
     private ObjectNode getDhcpRelayServersJsonOutput() {
         ObjectNode node = mapper().createObjectNode();
-        node.put("Default-DHCP-Servers", getDefaultDhcpServers());
-        node.put("Indirect-DHCP-Servers", getIndirectDhcpServers());
-        node.put("DHCP-Relay-Records([D]:Directly-Connected)", dhcpRelayRecords());
+        if (getDefaultDhcpServers().size() != 0) {
+            node.put("Default-DHCP-Servers", getDefaultDhcpServers());
+        }
+        if (getIndirectDhcpServers().size() != 0) {
+            node.put("Indirect-DHCP-Servers", getIndirectDhcpServers());
+        }
+        if (dhcpRelayRecords().size() != 0) {
+            node.put("DHCP-Relay-Records", dhcpRelayRecords());
+        }
         return node;
     }