[scala][client]: scala-http4s scala3 client: minor improvement (allow empty string in optional enum to pass as None) (#21025)

* [scala][http4s][client]: add enum method; remove implicit

* improve error handling

* more enum enhancement

* remove unused

* update samle

* avoid breaking change

* [Scala][Client][HTTP4s]: when enum is optional, avoid throwing exception when it's empty string

---------

Co-authored-by: Jenny Leahy <jennyleahy@JENNYLEAHY.localdomain>
Co-authored-by: Jenny Leahy <jennyleahy@Mac.localdomain>

modules/openapi-generator/src/main/resources/scala-http4s/model.mustache

@@ -56,7 +56,7 @@ object {{classname}} {
   given decoder{{classname}}: Decoder[{{classname}}] = Decoder.instance { c =>
     for {
       {{#vars}}
-      {{name}} <- c.downField("{{baseName}}").as[{{^required}}Option[{{{dataType}}}]{{/required}}{{#required}}{{{dataType}}}{{/required}}]
+      {{name}} <- {{#isEnumOrRef}}{{^required}}mapEmptyStringToNull(c.downField("{{baseName}}")){{/required}}{{#required}}c.downField("{{baseName}}"){{/required}}{{/isEnumOrRef}}{{^isEnumOrRef}}c.downField("{{baseName}}"){{/isEnumOrRef}}.as[{{^required}}Option[{{{dataType}}}]{{/required}}{{#required}}{{{dataType}}}{{/required}}]
       {{/vars}}
     } yield {{classname}}(
       {{#vars}}

modules/openapi-generator/src/main/resources/scala-http4s/modelsPackage.mustache

@@ -1,7 +1,7 @@
 {{>licenseInfo}}
 package {{packageName}}
 
-import io.circe.{Decoder, Encoder, Json}
+import io.circe.{Decoder, Encoder, Json, ACursor}
 import java.time.{Instant, LocalDate, OffsetDateTime}
 import java.util.UUID
 
@@ -31,4 +31,7 @@ package object models {
   given encodeJson: Encoder[Json] =
     Encoder.encodeString.contramap[Json](_.toString)
 
+  def mapEmptyStringToNull(f: ACursor): ACursor =
+    f.withFocus(json => if json.toString == "\"\"" then Json.Null else json)
+
 }

samples/client/petstore/scala-http4s/src/main/scala/org/openapitools/client/models/Order.scala

@@ -52,7 +52,7 @@ object Order {
       petId <- c.downField("petId").as[Option[Long]]
       quantity <- c.downField("quantity").as[Option[Int]]
       shipDate <- c.downField("shipDate").as[Option[Instant]]
-      status <- c.downField("status").as[Option[OrderStatus]]
+      status <- mapEmptyStringToNull(c.downField("status")).as[Option[OrderStatus]]
       complete <- c.downField("complete").as[Option[Boolean]]
     } yield Order(
       id = id,

samples/client/petstore/scala-http4s/src/main/scala/org/openapitools/client/models/Pet.scala

@@ -53,7 +53,7 @@ object Pet {
       name <- c.downField("name").as[String]
       photoUrls <- c.downField("photoUrls").as[Seq[String]]
       tags <- c.downField("tags").as[Option[Seq[Tag]]]
-      status <- c.downField("status").as[Option[PetStatus]]
+      status <- mapEmptyStringToNull(c.downField("status")).as[Option[PetStatus]]
     } yield Pet(
       id = id,
       category = category,

samples/client/petstore/scala-http4s/src/main/scala/org/openapitools/client/models/package.scala

@@ -10,7 +10,7 @@
   */
 package org.openapitools.client
 
-import io.circe.{Decoder, Encoder, Json}
+import io.circe.{Decoder, Encoder, Json, ACursor}
 import java.time.{Instant, LocalDate, OffsetDateTime}
 import java.util.UUID
 
@@ -40,4 +40,7 @@ package object models {
   given encodeJson: Encoder[Json] =
     Encoder.encodeString.contramap[Json](_.toString)
 
+  def mapEmptyStringToNull(f: ACursor): ACursor =
+    f.withFocus(json => if json.toString == "\"\"" then Json.Null else json)
+
 }