pass a nullable optional value instead of null as it is dereferenced in the called function without a null check

Change-Id: I723cfd469de3e3d5392445371b7736d0d59c31bf
diff --git a/app/src/main/java/org/opencord/dhcpl2relay/impl/DhcpL2Relay.java b/app/src/main/java/org/opencord/dhcpl2relay/impl/DhcpL2Relay.java
index ba4bf1a..4bc4ca8 100755
--- a/app/src/main/java/org/opencord/dhcpl2relay/impl/DhcpL2Relay.java
+++ b/app/src/main/java/org/opencord/dhcpl2relay/impl/DhcpL2Relay.java
@@ -1149,7 +1149,7 @@
                         if (useOltUplink && isUplinkPortOfOlt(event.subject().id(), event.port())) {
                             requestDhcpPacketsFromConnectPoint(
                                 new ConnectPoint(event.subject().id(), event.port().number()),
-                                null);
+                                        Optional.ofNullable(null));
                         }
                         break;
                     default: