in bigquery/src/main/scala/magnolify/bigquery/TableRowType.scala [226:233]
override protected def buildSchema(cm: CaseMapper): TableFieldSchema =
f.fieldSchema(cm).clone().setMode("NULLABLE")
override def from(v: f.FromT)(cm: CaseMapper): Option[T] =
if (v == null) None else Some(f.from(v)(cm))
override def to(v: Option[T])(cm: CaseMapper): f.ToT = v match {
case None => null.asInstanceOf[f.ToT]
case Some(x) => f.to(x)(cm)
}