diff --git a/hyracks/hyracks-dataflow-std/src/main/java/org/apache/hyracks/dataflow/std/group/external/ExternalGroupBuildOperatorNodePushable.java b/hyracks/hyracks-dataflow-std/src/main/java/org/apache/hyracks/dataflow/std/group/external/ExternalGroupBuildOperatorNodePushable.java
index ba3853c..852a160 100644
--- a/hyracks/hyracks-dataflow-std/src/main/java/org/apache/hyracks/dataflow/std/group/external/ExternalGroupBuildOperatorNodePushable.java
+++ b/hyracks/hyracks-dataflow-std/src/main/java/org/apache/hyracks/dataflow/std/group/external/ExternalGroupBuildOperatorNodePushable.java
@@ -71,7 +71,8 @@
         for (int i = 0; i < comparatorFactories.length; ++i) {
             comparators[i] = comparatorFactories[i].createBinaryComparator();
         }
-        this.firstNormalizerComputer = firstNormalizerFactory.createNormalizedKeyComputer();
+        this.firstNormalizerComputer = firstNormalizerFactory == null ? null
+                : firstNormalizerFactory.createNormalizedKeyComputer();
         this.spillableTableFactory = spillableTableFactory;
         this.inRecordDescriptor = inRecordDescriptor;
         this.outRecordDescriptor = outRecordDescriptor;
diff --git a/hyracks/hyracks-dataflow-std/src/main/java/org/apache/hyracks/dataflow/std/group/external/ExternalGroupWriteOperatorNodePushable.java b/hyracks/hyracks-dataflow-std/src/main/java/org/apache/hyracks/dataflow/std/group/external/ExternalGroupWriteOperatorNodePushable.java
index a2922ae..0dbb063 100644
--- a/hyracks/hyracks-dataflow-std/src/main/java/org/apache/hyracks/dataflow/std/group/external/ExternalGroupWriteOperatorNodePushable.java
+++ b/hyracks/hyracks-dataflow-std/src/main/java/org/apache/hyracks/dataflow/std/group/external/ExternalGroupWriteOperatorNodePushable.java
@@ -64,7 +64,7 @@
         this.stateId = stateId;
         this.spillableTableFactory = spillableTableFactory;
         this.frameLimit = framesLimit;
-        this.nmkComputer = nmkFactory.createNormalizedKeyComputer();
+        this.nmkComputer = nmkFactory == null ? null : nmkFactory.createNormalizedKeyComputer();
 
         this.partialAggRecordDesc = partialAggRecordDesc;
         this.outRecordDesc = outRecordDesc;