The row length used to initialize DataSetTumbleTimeWindowAggReduceGroupFunction was not set properly. (I think this is introduced by mistake when merging the code).
We currently lack the built-in non-partial-merge Aggregates. Therefore this has not been captured by the unit test.
1. set the "supportPartial" to false for SumAggregate
2. Then both testAllEventTimeTumblingWindowOverTime and testEventTimeTumblingGroupWindowOverTime will fail.