It seems like

Row::getNotNull

doesn't return fields that are supposed to be wrapped in a

value class

in fromTemplate... I wonder if there's any way to make it wrap the value when a value class is needed...? It would make this more consistent with the behaviour for value classes elsewhere...

fromTemplate

and

Row

are low-level APIs that do not wisely convert ValueClasses. It would be better to create your extension function as follows:

fun Row.getYourValueClassNotNull(columnLabel: String): YourValueClass {
    ...
}