problem the same as in PDI-9662, but for "group by" step
"Memory Group by" step - Minimum aggregation doesn't work
Group by: "Minimum" aggregation function returns null even if non-null values are present
Denormaliser step: Minimum Aggregation with multiple columns carries data across columns
Group by and Memory group by ignores NULL values ("sum" aggregation)
Denormalizer step: Minimum aggregation doesn't work
Group by step - Minimum aggregation doesn't work when null value in first row.
Denormaliser step: KettleValueException on Minimum Aggregation only