diff --git a/application/src/main/java/org/thingsboard/server/service/cf/ctx/state/aggregation/function/CountUniqueAggEntry.java b/application/src/main/java/org/thingsboard/server/service/cf/ctx/state/aggregation/function/CountUniqueAggEntry.java
index 3c14d7c9b9..90587fce27 100644
--- a/application/src/main/java/org/thingsboard/server/service/cf/ctx/state/aggregation/function/CountUniqueAggEntry.java
+++ b/application/src/main/java/org/thingsboard/server/service/cf/ctx/state/aggregation/function/CountUniqueAggEntry.java
@@ -17,12 +17,13 @@ package org.thingsboard.server.service.cf.ctx.state.aggregation.function;
 
 import org.thingsboard.server.common.data.cf.configuration.aggregation.AggFunction;
 
+import java.util.HashSet;
 import java.util.Optional;
 import java.util.Set;
 
 public class CountUniqueAggEntry implements AggEntry {
 
-    private Set<String> items;
+    private final Set<String> items = new HashSet<>();
 
     @Override
     public void update(Object value) {