could not find Lazy implicit value of type io.circe.generic.extras.decoding.Configured(Decoder|Encoder)[A]

circe.scala

sealed trait T

object T {

  object X {

    case class T1(foo: String)
    case class T2(bar: String)
  }
}

import io.circe._
import io.circe.syntax._
import io.circe.generic.extras.Configuration
import io.circe.generic.extras.semiauto._

object Json {

  implicit val config = Configuration.default

  val decodeT: Decoder[T] =
    deriveDecoder

  val encodeT: Encoder[T] =
    deriveEncoder
}