Add StringEnum JSON converters for batch jobs

src/Stripe.net/Infrastructure/JsonConverters/NewtonsoftStringEnumConverter.cs

@@ -0,0 +1,35 @@
+namespace Stripe.Infrastructure
+{
+    using System;
+    using Newtonsoft.Json;
+
+    /// <summary>
+    /// Newtonsoft converter that serializes any <see cref="StringEnum"/>
+    /// subclass as its <see cref="StringEnum.Value"/> string.
+    /// </summary>
+    internal class NewtonsoftStringEnumConverter : JsonConverter
+    {
+        public override bool CanConvert(Type objectType)
+        {
+            return typeof(StringEnum).IsAssignableFrom(objectType);
+        }
+
+        public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
+        {
+            if (value == null)
+            {
+                writer.WriteNull();
+            }
+            else
+            {
+                writer.WriteValue(((StringEnum)value).Value);
+            }
+        }
+
+        public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
+        {
+            throw new NotSupportedException(
+                $"Deserialization of {objectType.Name} (StringEnum) is not supported.");
+        }
+    }
+}

src/Stripe.net/Infrastructure/JsonConverters/STJStringEnumConverterFactory.cs

@@ -0,0 +1,46 @@
+namespace Stripe.Infrastructure
+{
+    using System;
+    using System.Text.Json;
+    using System.Text.Json.Serialization;
+
+    /// <summary>
+    /// STJ converter factory that serializes any <see cref="StringEnum"/>
+    /// subclass as its <see cref="StringEnum.Value"/> string.
+    /// </summary>
+    internal class STJStringEnumConverterFactory : JsonConverterFactory
+    {
+        public override bool CanConvert(Type typeToConvert)
+        {
+            return typeof(StringEnum).IsAssignableFrom(typeToConvert);
+        }
+
+        public override JsonConverter CreateConverter(Type typeToConvert, JsonSerializerOptions options)
+        {
+            return (JsonConverter)Activator.CreateInstance(
+                typeof(STJStringEnumConverterInner<>).MakeGenericType(typeToConvert));
+        }
+
+        private class STJStringEnumConverterInner<T> : JsonConverter<T>
+            where T : StringEnum
+        {
+            public override T Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+            {
+                throw new NotSupportedException(
+                    $"Deserialization of {typeToConvert.Name} (StringEnum) is not supported.");
+            }
+
+            public override void Write(Utf8JsonWriter writer, T value, JsonSerializerOptions options)
+            {
+                if (value == null)
+                {
+                    writer.WriteNullValue();
+                }
+                else
+                {
+                    writer.WriteStringValue(value.Value);
+                }
+            }
+        }
+    }
+}

src/Stripe.net/Services/Invoices/UpcomingInvoiceSubscriptionResumeAt.cs

@@ -1,5 +1,8 @@
 namespace Stripe
 {
+    using STJS = System.Text.Json.Serialization;
+
+    [STJS.JsonConverter(typeof(Infrastructure.STJStringEnumConverterFactory))]
     public class UpcomingInvoiceSubscriptionResumeAt : StringEnum
     {
         /// <summary>When viewing an upcoming invoice for a subscription, simulates it resuming to the current time.</summary>

src/Stripe.net/Services/Subscriptions/SubscriptionBillingCycleAnchor.cs

@@ -1,5 +1,8 @@
 namespace Stripe
 {
+    using STJS = System.Text.Json.Serialization;
+
+    [STJS.JsonConverter(typeof(Infrastructure.STJStringEnumConverterFactory))]
     public class SubscriptionBillingCycleAnchor : StringEnum
     {
         /// <summary>Resets the subscription's billing cycle anchor to the current time.</summary>

src/Stripe.net/Services/_base/StringEnum.cs

@@ -1,7 +1,5 @@
 namespace Stripe
 {
-    using System.Text.Json.Serialization;
-
     /// <summary>
     /// Abstract base class for string enum parameters.
     /// </summary>
@@ -25,6 +23,8 @@ namespace Stripe
     /// }
     /// </code>
     /// </example>
+    [Newtonsoft.Json.JsonConverter(typeof(Infrastructure.NewtonsoftStringEnumConverter))]
+    [NoSystemTextJsonAttributesNeeded("STJ converter is on each concrete subclass because STJ does not inherit converter attributes from base classes.")]
     public abstract class StringEnum
     {
         /// <summary>Initializes a new instance of the <see cref="StringEnum"/> class.</summary>
@@ -36,7 +36,7 @@ protected StringEnum(string value)
 
         /// <summary>Gets or sets the serialized value.</summary>
         /// <returns>The serialized value.</returns>
-        [JsonPropertyName("Value")]
+        [System.Text.Json.Serialization.JsonPropertyName("Value")]
         public string Value { get; protected set; }
 
         /// <summary>Returns the serialized value.</summary>