json4s“无法将JString(2019-04-28T01:23:45.678Z)转换为类java.time.Instant"？

import org.json4s._
import org.json4s.jackson.JsonMethods._
import java.time.Instant
import java.time.format.DateTimeFormatter

// 自定义序列化器
class InstantSerializer extends CustomSerializer[Instant](format => (
  {
    case JString(str) => Instant.parse(str)
  },
  {
    case instant: Instant => JString(DateTimeFormatter.ISO_INSTANT.format(instant))
  }
))

// 注册自定义序列化器
implicit val formats: Formats = DefaultFormats + new InstantSerializer

// JSON字符串
val jsonString = """{"timestamp": "2019-04-28T01:23:45.678Z"}"""

// 解析JSON
val json = parse(jsonString)

// 提取Instant字段
val timestamp = (json \ "timestamp").extract[Instant]

// 打印结果
println(timestamp)