def registerKryoClasses(classes: Array[Class[_]]): SparkConf = { .. }

@transient lazy val conf: RuntimeConfig = new RuntimeConfig(sessionState.conf)

/**
 * Runtime configuration interface for Spark. To access this, use `SparkSession.conf`.
 *
 * Options set here are automatically propagated to the Hadoop configuration during I/O.
 *
 * @since 2.0.0
 */
@InterfaceStability.Stable
class RuntimeConfig private[sql](sqlConf: SQLConf = new SQLConf) {

val mysparkConf = SparkConf.set(someKey,someVal)
SparkSession.builder.conf(mySparkConf)

sparkConf.registerKryoClasses(Array(classOf[org.apache.spark.sql.Row]))

scala>   spark.conf.registerKryoClasses(Array(classOf[Row]))

implicit val generalRowEncoder: Encoder[Row] = org.apache.spark.sql.Encoders.kryo[Row]