Fix aggregate queries without explicit grouping

fdb-record-layer-core/src/main/java/com/apple/foundationdb/record/cursors/aggregate/StreamGrouping.java

@@ -116,10 +116,12 @@ public StreamGrouping(@Nullable final Value groupingKeyValue,
             this.accumulator = aggregateValue.createAccumulatorWithInitialState(context.getTypeRepository(), null);
         } else {
             this.accumulator = aggregateValue.createAccumulatorWithInitialState(context.getTypeRepository(), partialAggregationResult.getAccumulatorStatesList());
-            try {
-                this.currentGroup = DynamicMessage.parseFrom(context.getTypeRepository().newMessageBuilder(groupingKeyValue.getResultType()).getDescriptorForType(), partialAggregationResult.getGroupKey().toByteArray());
-            } catch (InvalidProtocolBufferException e) {
-                throw new RuntimeException(e);
+            if (groupingKeyValue != null) {
+                try {
+                    this.currentGroup = DynamicMessage.parseFrom(context.getTypeRepository().newMessageBuilder(groupingKeyValue.getResultType()).getDescriptorForType(), partialAggregationResult.getGroupKey().toByteArray());
+                } catch (InvalidProtocolBufferException e) {
+                    throw new RuntimeException(e);
+                }
             }
         }
         this.store = store;
@@ -212,16 +214,18 @@ private Object evalGroupingKey(@Nullable final Object currentObject) {
 
     @Nullable
     public RecordCursorProto.PartialAggregationResult getPartialAggregationResult() {
-        if (currentGroup == null) {
+        if (groupingKeyValue != null && currentGroup == null) {
             return null;
         }
         List<RecordCursorProto.AccumulatorState> accumulatorStates = accumulator.getAccumulatorStates();
         if (accumulatorStates.isEmpty()) {
             return null;
         }
-        return RecordCursorProto.PartialAggregationResult.newBuilder()
-                .setGroupKey(Objects.requireNonNull((Message)currentGroup).toByteString())
-                .addAllAccumulatorStates(accumulatorStates)
-                .build();
+        final RecordCursorProto.PartialAggregationResult.Builder builder = RecordCursorProto.PartialAggregationResult.newBuilder()
+                .addAllAccumulatorStates(accumulatorStates);
+        if (groupingKeyValue != null) {
+            builder.setGroupKey(Objects.requireNonNull((Message)currentGroup).toByteString());
+        }
+        return builder.build();
     }
 }

yaml-tests/src/test/resources/aggregate-ungrouped-continuation.yamsql

@@ -0,0 +1,62 @@
+#
+# aggregate-ungrouped-continuation.yamsql
+#
+# This source file is part of the FoundationDB open source project
+#
+# Copyright 2021-2024 Apple Inc. and the FoundationDB project authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# Regression test for aggregate queries without explicit GROUP BY
+# that use continuations (maxRows). Previously, resuming from a
+# continuation with no grouping key caused a NullPointerException
+# in StreamGrouping when groupingKeyValue was null.
+
+---
+schema_template:
+    create table t1(id bigint, col1 bigint, col2 bigint, primary key(id))
+    create index mv1 as select sum(col2) from t1 group by col1
+---
+setup:
+  steps:
+    - query: INSERT INTO T1
+        VALUES (1, 10, 1),
+               (2, 10, 2),
+               (3, 10, 3),
+               (4, 20, 4),
+               (5, 20, 5),
+               (6, 20, 6)
+---
+test_block:
+  name: aggregate-ungrouped-continuation
+  tests:
+    -
+      # Aggregate without GROUP BY, no continuation needed (single result row)
+      - query: select sum(col2) from t1
+      - result: [{!l 21}]
+    -
+      # Aggregate without GROUP BY with maxRows=1 to force continuation.
+      # This triggered a NullPointerException before the fix because
+      # getPartialAggregationResult tried to serialize a null currentGroup.
+      - query: select sum(col2) from t1
+      - maxRows: 1
+      - result: [{!l 21}]
+      - result: []
+    -
+      # Aggregate with GROUP BY and maxRows=1 to verify continuations
+      # still work correctly with grouping keys present.
+      - query: select col1, sum(col2) from t1 group by col1
+      - maxRows: 1
+      - result: [{!l 10, !l 6}]
+      - result: [{!l 20, !l 15}]
+      - result: []