Let's say we have
val df = dataFrameOf("a")("a")
val counted = df.drop(1).groupBy { a }.count()
or
val counted = df.drop(1).groupBy { a }.aggregate { count() into "count" }
In this case counted does not obtain the column count, it just has the empty column a.
This is an issue, because the compiler plugin cannot tell a dataframe is empty, so it will happily suggest .count and cause runtime exceptions:
We should at least get an empty Int column count in this case.
Thanks for the find @Allex-Nik!