is there a better way to write that:

kotlin
fun getCitation(code: String, offset: Int = 0): Citation? {
        var result: Citation? = null
        transaction(db) {
            result = Citation.wrapRows(Citations
                .select { Citations.code eq code }.limit(1)).toList().getOrNull(0)
        }
        return result
    }

Without knowing more about your code, I created a generalized solution that is similar to ones we are using in one of our current projects. This may give you some ideas for how to structure it. Of course, there are most likely other ways, and I have only been using Kotlin for 4-5 months.

object Citations : IntIdTable("citations") {
    data class Citation(val id: Int, val code: String, val citation: String)

    val code = text("code").uniqueIndex()
    val citation = text("citation")

    private fun toCitation(row: ResultRow): Citation =
        Citation(
            row[Citations.id].value,
            row[Citations.code],
            row[Citations.citation]
        )

    fun getCitation(code: String): Citation? =
        transaction {
            Citations.select { Citations.code eq code }
                .mapNotNull { toCitation(it) }
                .singleOrNull()
        }
}

@bjonnh, maybe

fun getCitation(code: String, offset: Int = 0): Citation? 
= transaction(db) {
    Citation.find { Citations.code eq code }.limit(1)).toList().singleOrNull()
    }