diff --git a/druid-hdrhistogram/src/main/java/org/apache/druid/query/aggregation/sketch/HdrHistogram/HdrHistogramAggregatorFactory.java b/druid-hdrhistogram/src/main/java/org/apache/druid/query/aggregation/sketch/HdrHistogram/HdrHistogramAggregatorFactory.java
index 679125f..85cc22d 100644
--- a/druid-hdrhistogram/src/main/java/org/apache/druid/query/aggregation/sketch/HdrHistogram/HdrHistogramAggregatorFactory.java
+++ b/druid-hdrhistogram/src/main/java/org/apache/druid/query/aggregation/sketch/HdrHistogram/HdrHistogramAggregatorFactory.java
@@ -214,6 +214,9 @@ public class HdrHistogramAggregatorFactory extends AggregatorFactory {
 
     @Override
     public Object deserialize(Object object) {
+        if (object == null) {
+            return null;
+        }
         return HistogramUtils.deserializeHistogram(object);
     }
 
diff --git a/druid-hlld/src/main/java/org/apache/druid/query/aggregation/sketch/hlld/HllAggregatorFactory.java b/druid-hlld/src/main/java/org/apache/druid/query/aggregation/sketch/hlld/HllAggregatorFactory.java
index a5d0e0d..fa68964 100644
--- a/druid-hlld/src/main/java/org/apache/druid/query/aggregation/sketch/hlld/HllAggregatorFactory.java
+++ b/druid-hlld/src/main/java/org/apache/druid/query/aggregation/sketch/hlld/HllAggregatorFactory.java
@@ -165,6 +165,9 @@ public class HllAggregatorFactory extends AggregatorFactory {
 
     @Override
     public Object deserialize(Object object) {
+        if (object == null) {
+            return null;
+        }
         return HllUtils.deserializeHll(object);
     }