Fix ConcurrentModificationException when processing PendingRemoveNextObjectives

Change-Id: Iaffad21812c86e26f0c9d44e39bc7e301c841bfe
diff --git a/drivers/default/src/main/java/org/onosproject/driver/pipeline/ofdpa/OfdpaGroupHandlerUtility.java b/drivers/default/src/main/java/org/onosproject/driver/pipeline/ofdpa/OfdpaGroupHandlerUtility.java
index 5e48ebf..b962153 100644
--- a/drivers/default/src/main/java/org/onosproject/driver/pipeline/ofdpa/OfdpaGroupHandlerUtility.java
+++ b/drivers/default/src/main/java/org/onosproject/driver/pipeline/ofdpa/OfdpaGroupHandlerUtility.java
@@ -705,13 +705,9 @@
                 keys.forEach(key -> groupHandler.processPendingUpdateNextObjs(key));
 
                 Set<GroupKey> k = Sets.newHashSet();
-                groupHandler.pendingRemoveNextObjectives
-                    .asMap().values().stream().forEach(keylist -> {
-                        k.addAll(keylist.stream()
-                                 .filter(key -> groupHandler.groupService
-                                         .getGroup(groupHandler.deviceId, key) == null)
-                                 .collect(Collectors.toSet()));
-                    });
+                groupHandler.pendingRemoveNextObjectives.asMap().values().forEach(keylist -> keylist.stream()
+                        .filter(key -> groupHandler.groupService.getGroup(groupHandler.deviceId, key) == null)
+                        .forEach(k::add));
                 k.forEach(key -> groupHandler.processPendingRemoveNextObjs(key));
 
             } catch (Exception exception) {