fix(isthmus): adding support for new proto and deprecated form in AggregateRel

core/src/main/java/io/substrait/relation/ProtoRelConverter.java

@@ -626,15 +626,40 @@ protected Aggregate newAggregate(AggregateRel rel) {
         new ProtoAggregateFunctionConverter(lookup, extensions, protoExprConverter);
 
     List<Aggregate.Grouping> groupings = new ArrayList<>(rel.getGroupingsCount());
-    for (AggregateRel.Grouping grouping : rel.getGroupingsList()) {
-      groupings.add(
-          Aggregate.Grouping.builder()
-              .expressions(
-                  grouping.getGroupingExpressionsList().stream()
-                      .map(protoExprConverter::from)
-                      .collect(java.util.stream.Collectors.toList()))
-              .build());
+
+    //       the deprecated form of Grouping is not used
+    if (!rel.getGroupingExpressionsList().isEmpty()) {
+      List<io.substrait.proto.Expression> allGroupingKeys = rel.getGroupingExpressionsList();
+
+      //          for every grouping object on aggregate, it has a list of references into the
+      // aggregate's expressionList for the specific sorting set
+      for (AggregateRel.Grouping grouping : rel.getGroupingsList()) {
+        List<io.substrait.proto.Expression> groupingKeys = new ArrayList<>();
+        for (int key : grouping.getExpressionReferencesList()) {
+          groupingKeys.add(allGroupingKeys.get(key));
+        }
+        groupings.add(
+            Aggregate.Grouping.builder()
+                .expressions(
+                    groupingKeys.stream()
+                        .map(protoExprConverter::from)
+                        .collect(Collectors.toList()))
+                .build());
+      }
+      Aggregate.builder().input(input).groupings(groupings);
+    } else {
+      //        using the deprecated form of Grouping and Aggregate
+      for (AggregateRel.Grouping grouping : rel.getGroupingsList()) {
+        groupings.add(
+            Aggregate.Grouping.builder()
+                .expressions(
+                    grouping.getGroupingExpressionsList().stream()
+                        .map(protoExprConverter::from)
+                        .collect(Collectors.toList()))
+                .build());
+      }
     }
+
     List<Aggregate.Measure> measures = new ArrayList<>(rel.getMeasuresCount());
     for (AggregateRel.Measure measure : rel.getMeasuresList()) {
       measures.add(