in core/src/main/scala/com/gu/marley/AvroSerialisable.scala [73:77]
override def writableValue(t: collection.Seq[T]): Any = t.map(w.writableValue).asJava
override def read(x: Any): collection.Seq[T] = x.asInstanceOf[java.util.List[Any]].asScala.map(w.read).toSeq
}
def SetAvroSerialisable[T](w: AvroSerialisable[T]) = new AvroSerialisable[scala.collection.Set[T]] {