on leftJoin TypeMapper for T is being applied on Option[T]

[NPCRUS]

having two tables wiith relation A.bId = B.id
on of witch has field of custom type T and therefore provided with TypeMapper for this custom type.

case class A[T[_]](id: T[Int], bId: T[Option[Int]])
object A extends Table[A]

enum Custom {
  case Foo, Bar
}
object Custom {
  given TypeMapper[Custom] = StringType.bimap(_.toString, Custom.valueOf)
}

case class B[T[_]](id: T[Int], custom: T[Custom])
object B extends Table[B]

having in database only records for table A, so in table B there are no records
and performing leftJoin on table B in such way:

A.select.leftJoin(B)(_.bId `=` _.id)

i get following error: enum Custom has no case with name: null
when in fact there are no records of table B and no custom field to perform type mapping on.

Expected result: it shouldn't try to serialize null into Custom, in fact there should be no value to serialize on at all

[NPCRUS]

what I found out is that in dialects a get method on type mapper for Enum is implemented in such manner:

def get(r: ResultSet, idx: Int): T = {
  val str = r.getString(idx)
  if (str == null) null.asInstanceOf[T]
  else constructor(str)
}

a hack that worked until I implemented my own type mapper for scala3 enums.
Another interesting thing here is that surprisingly type mapping for Options doesn't stop at None, even though type mapper for options is defined like this:

def get(r: ResultSet, idx: Int): Option[T] = {
  if (r.getObject(idx) == null) None else Some(inner.get(r, idx))
}

where inner is TypeMapper[T]