Remove unnecessary error generation when JsUndefined.asOpt is used (#1112)

* Removed unnecessary error generation in the JsUndefined class when the asOpt function was used

* Added test for JsUndefined.asOpt function

* Formatting

Author: Dubinka94

play-json/shared/src/main/scala/play/api/libs/json/JsLookup.scala

@@ -195,9 +195,10 @@ case class JsDefined(value: JsValue) extends AnyVal with JsLookupResult
  * Represent a missing Json value.
  */
 final class JsUndefined(err: => String) extends JsLookupResult {
-  def error             = err
-  def validationError   = JsonValidationError(error)
-  override def toString = s"JsUndefined($err)"
+  def error                                                = err
+  def validationError                                      = JsonValidationError(error)
+  override def toString                                    = s"JsUndefined($err)"
+  override def asOpt[T](implicit fjs: Reads[T]): Option[T] = None
 }
 
 object JsUndefined {

play-json/shared/src/test/scala/play/api/libs/json/JsLookupSpec.scala

@@ -0,0 +1,27 @@
+/*
+ * Copyright (C) from 2022 The Play Framework Contributors <https://github.com/playframework>, 2011-2021 Lightbend Inc. <https://www.lightbend.com>
+ */
+
+package play.api.libs.json
+
+import play.api.libs.json.Json._
+
+import org.scalatest.matchers.must.Matchers
+import org.scalatest.wordspec.AnyWordSpec
+
+class JsLookupSpec extends AnyWordSpec with Matchers {
+  "JsLookupResult" should {
+    val obj = Json.obj(
+      "field" -> 123
+    )
+    val result = obj \ "missingField"
+
+    "return JsUndefined when a key is missing" in {
+      result mustBe a[JsUndefined]
+    }
+
+    "return None when calling asOpt on JsUndefined" in {
+      result.asOpt[Int].mustEqual(None)
+    }
+  }
+}