diff --git a/asterix-algebra/src/main/java/edu/uci/ics/asterix/optimizer/base/RuleCollections.java b/asterix-algebra/src/main/java/edu/uci/ics/asterix/optimizer/base/RuleCollections.java
index b6cc194..49045f0 100644
--- a/asterix-algebra/src/main/java/edu/uci/ics/asterix/optimizer/base/RuleCollections.java
+++ b/asterix-algebra/src/main/java/edu/uci/ics/asterix/optimizer/base/RuleCollections.java
@@ -63,7 +63,6 @@
 import edu.uci.ics.hyracks.algebricks.rewriter.rules.InsertProjectBeforeUnionRule;
 import edu.uci.ics.hyracks.algebricks.rewriter.rules.IntroHashPartitionMergeExchange;
 import edu.uci.ics.hyracks.algebricks.rewriter.rules.IntroJoinInsideSubplanRule;
-import edu.uci.ics.hyracks.algebricks.rewriter.rules.IntroduceCombinerRule;
 import edu.uci.ics.hyracks.algebricks.rewriter.rules.IntroduceGroupByForSubplanRule;
 import edu.uci.ics.hyracks.algebricks.rewriter.rules.IsolateHyracksOperatorsRule;
 import edu.uci.ics.hyracks.algebricks.rewriter.rules.PullSelectOutOfEqJoin;
@@ -93,6 +92,8 @@
     public final static List<IAlgebraicRewriteRule> buildNormalizationRuleCollection() {
         List<IAlgebraicRewriteRule> normalization = new LinkedList<IAlgebraicRewriteRule>();
         normalization.add(new EliminateSubplanRule());
+        // TODO: The IntroduceGroupByForStandaloneAggregRule performs an invalid rewrite, and we've replaced it
+        // with PushAggFuncIntoStandaloneAggregateRule. Wee need more testing before we can remove it complete.y
         //normalization.add(new IntroduceGroupByForStandaloneAggregRule());
         normalization.add(new PushAggFuncIntoStandaloneAggregateRule());
         normalization.add(new BreakSelectIntoConjunctsRule());
@@ -167,7 +168,7 @@
         consolidation.add(new ConsolidateSelectsRule());
         consolidation.add(new ConsolidateAssignsRule());
         consolidation.add(new InlineAssignIntoAggregateRule());
-        consolidation.add(new IntroduceCombinerRule());
+        //consolidation.add(new IntroduceCombinerRule());
         consolidation.add(new CountVarToCountOneRule());
         consolidation.add(new IntroduceSelectAccessMethodRule());
         consolidation.add(new IntroduceJoinAccessMethodRule());
diff --git a/asterix-runtime/src/main/java/edu/uci/ics/asterix/runtime/aggregates/std/SumAggregateDescriptor.java b/asterix-runtime/src/main/java/edu/uci/ics/asterix/runtime/aggregates/std/SumAggregateDescriptor.java
index 5e45432..468def7 100644
--- a/asterix-runtime/src/main/java/edu/uci/ics/asterix/runtime/aggregates/std/SumAggregateDescriptor.java
+++ b/asterix-runtime/src/main/java/edu/uci/ics/asterix/runtime/aggregates/std/SumAggregateDescriptor.java
@@ -185,6 +185,9 @@
                                 aInt8.setValue((byte) sum);
                                 serde.serialize(aInt8, out);
                             } else {
+                            	serde = AqlSerializerDeserializerProvider.INSTANCE
+                                        .getSerializerDeserializer(BuiltinType.ANULL);
+                                serde.serialize(ANull.NULL, out);
                                 GlobalConfig.ASTERIX_LOGGER.fine("SUM aggregate ran over empty input.");
                             }