Failing GQL mutation

test.scala

import sangria.schema._
import sangria.execution._
import sangria.marshalling.sprayJson._
import sangria.parser.QueryParser
import spray.json._
import scala.concurrent.duration._
import scala.concurrent.Await
import scala.concurrent.ExecutionContext.Implicits.global
import sangria.macros.derive.deriveInputObjectType

case class Ctx()
case class ContactInput(name: String)

object MyJsonProtocol extends DefaultJsonProtocol {
  implicit val contactInput: RootJsonFormat[ContactInput] = jsonFormat1(ContactInput.apply)
}

import MyJsonProtocol._

// The schema

val ContactInputType: InputType[ContactInput] = deriveInputObjectType[ContactInput]()

val submit: Field[Ctx, Unit] = Field("submit", StringType,
  arguments = Argument("contacts", ListInputType(ContactInputType)) :: Nil,
  resolve = c => "hello" + c.arg("contacts")
)

// Schema root
val Mutation: ObjectType[Ctx, Unit] = ObjectType("Mutation", fields[Ctx, Unit](submit))
val Query: ObjectType[Ctx, Unit] = ObjectType("Query", fields[Ctx, Unit](
  Field("hello", StringType, resolve = _ ⇒ "Hello world!")
))
val schema = Schema(Query, Some(Mutation))

// Test mutation
val query = """
  mutation {submit(contacts:[{name: "Test"}])}
"""

val result = Executor.execute(
  schema,
  QueryParser.parse(query).get,
  userContext = Ctx(),
)
println(Await.result(result, 10.seconds))

// Expected output:
//
//   {
//     "hello": "helloVector(...."
//   }

// Actual output:
// 
// java.lang.ClassCastException: scala.collection.immutable.Vector cannot be cast to spray.json.JsValue
//	at sangria.marshalling.sprayJson$$anon$2.fromResult(scratch.scala:99)
//	at sangria.execution.ValueCollector$.$anonfun$getArgumentValues$6(scratch.scala:86)