使用json4s序列化可选值类实例时出现问题

import org.json4s._
import org.json4s.native.Serialization
import org.json4s.native.Serialization.{read, write}

case class MyClass(value: Option[String])

class MyClassSerializer extends CustomSerializer[MyClass](format => (
  {
    case JObject(JField("value", JString(v)) :: Nil) => MyClass(Some(v))
    case JObject(JField("value", JNull) :: Nil) => MyClass(None)
  },
  {
    case MyClass(Some(v)) => JObject(JField("value", JString(v)))
    case MyClass(None) => JObject(JField("value", JNull))
  }
))

implicit val formats = DefaultFormats + new MyClassSerializer

val myObj = MyClass(Some("example"))
val json = write(myObj)
val deserializedObj = read[MyClass](json)

import org.json4s._
import org.json4s.native.Serialization
import org.json4s.native.Serialization.{read, write}

case class MyClass(value: Option[String])

class MyClassDeserializer extends CustomDeserializer[MyClass](format => (
  {
    case JObject(JField("value", JString(v)) :: Nil) => MyClass(Some(v))
    case JObject(JField("value", JNull) :: Nil) => MyClass(None)
  }
))

implicit val formats = DefaultFormats + new MyClassDeserializer

val json = """{"value": null}"""
val deserializedObj = read[MyClass](json)