From 3a1d922d817fe570a34ce94bf5ec3214369d5af8 Mon Sep 17 00:00:00 2001
From: Jakob Odersky <jakob@odersky.com>
Date: Thu, 29 Mar 2018 13:11:43 -0700
Subject: Allow deserialization of optional fields if they are omitted

Fixes #5
---
 build.sbt                                   |  2 +-
 src/main/scala/DerivedFormats.scala         |  7 ++++++-
 src/test/scala/ProductTypeFormatTests.scala | 17 +++++++++++++++++
 3 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/build.sbt b/build.sbt
index 23c577f..5d595be 100644
--- a/build.sbt
+++ b/build.sbt
@@ -17,7 +17,7 @@ scalacOptions ++= Seq(
 
 libraryDependencies ++= Seq(
   "io.spray" %% "spray-json" % "1.3.4",
-  "com.propensive" %% "magnolia" % "0.7.1",
+  "com.propensive" %% "magnolia" % "0.7.2-SNAPSHOT",
   "org.scalatest" %% "scalatest" % "3.0.2" % "test"
 )
 
diff --git a/src/main/scala/DerivedFormats.scala b/src/main/scala/DerivedFormats.scala
index d0cac38..5bba08a 100644
--- a/src/main/scala/DerivedFormats.scala
+++ b/src/main/scala/DerivedFormats.scala
@@ -24,7 +24,12 @@ trait DerivedFormats { self: BasicFormats =>
             ctx.rawConstruct(Seq.empty)
           } else {
             ctx.construct { param =>
-              param.typeclass.read(obj.fields(param.label))
+              val fieldValue = if (param.isOption) {
+                obj.fields.getOrElse(param.label, JsNull)
+              } else {
+                obj.fields(param.label)
+              }
+              param.typeclass.read(fieldValue)
             }
           }
         case js =>
diff --git a/src/test/scala/ProductTypeFormatTests.scala b/src/test/scala/ProductTypeFormatTests.scala
index ce05000..d602ff4 100644
--- a/src/test/scala/ProductTypeFormatTests.scala
+++ b/src/test/scala/ProductTypeFormatTests.scala
@@ -74,4 +74,21 @@ class ProductTypeFormatTests
     """{"h": {"x":true}}"""
   )
 
+  case class Opt(x: Option[Int])
+  implicit val ofmt = jsonFormat[Opt]
+
+  "Optional fields with some value" should behave like checkRoundtrip(
+    Opt(Some(2)),
+    """{"x":2}"""
+  )
+
+  "Optional fields with no value (null)" should behave like checkRoundtrip(
+    Opt(None),
+    """{"x":null}"""
+  )
+
+  "Optional fields with no value (undefined)" should "deserialize" in {
+    assert("{}".parseJson.convertTo[Opt] == Opt(None))
+  }
+
 }
-- 
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