Posted by Timo Walther on URL: http://deprecated-apache-flink-user-mailing-list-archive.369.s1.nabble.com/The-way-to-write-a-UDF-with-generic-type-tp25329p25392.html
Currently, this functionality is hard-coded in the aggregation
translation. Namely in
`org.apache.flink.table.runtime.aggregate.AggregateUtil#transformToAggregateFunctions`
[1].