Play Json: Json.writes[T] 和 Json.obj 对 Option 的处理不一致

PlayJsonTest.scala

import org.scalatest.{ShouldMatchers, FunSpec}
import play.api.libs.json.Json

case class A(a: String, b: Option[String], c: Option[Int])

class PlayJsonTest extends FunSpec with ShouldMatchers {
  implicit val __aWrites = Json.writes[A]

  val result = """{"a":"a","c":1}"""

  describe("PlayJson") {
    it("writes") {
      val a = Json.toJson(A("a", None, Some(1)))
      Json.stringify(a) shouldBe result
    }

    it("obj") {
      val a = Json.obj("a" -> "a", "b" -> Option.empty[String], "c" -> 1)
      Json.stringify(a) shouldBe result
    }
  }
}