diff --git a/docs/content/misc/tasks.md b/docs/content/misc/tasks.md
index beaa2ba6d36..8c116e248f2 100644
--- a/docs/content/misc/tasks.md
+++ b/docs/content/misc/tasks.md
@@ -294,6 +294,7 @@ Merge tasks merge a list of segments together. Any common timestamps are merged.
     "type": "merge",
     "id": <task_id>,
     "dataSource": <task_datasource>,
+    "aggregations": <list of aggregators>,
     "segments": <JSON list of DataSegment objects to merge>
 }
 ```
diff --git a/indexing-service/src/main/java/io/druid/indexing/common/task/MergeTask.java b/indexing-service/src/main/java/io/druid/indexing/common/task/MergeTask.java
index 543accff499..ebf86904d06 100644
--- a/indexing-service/src/main/java/io/druid/indexing/common/task/MergeTask.java
+++ b/indexing-service/src/main/java/io/druid/indexing/common/task/MergeTask.java
@@ -21,6 +21,7 @@ import com.fasterxml.jackson.annotation.JsonCreator;
 import com.fasterxml.jackson.annotation.JsonIgnore;
 import com.fasterxml.jackson.annotation.JsonProperty;
 import com.google.common.base.Function;
+import com.google.common.base.Preconditions;
 import com.google.common.base.Throwables;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.Lists;
@@ -56,7 +57,7 @@ public class MergeTask extends MergeTaskBase
   )
   {
     super(id, dataSource, segments, context);
-    this.aggregators = aggregators;
+    this.aggregators = Preconditions.checkNotNull(aggregators, "null aggregations");
     this.indexSpec = indexSpec == null ? new IndexSpec() : indexSpec;
   }