From a75a17f3cd68a6ec0b9a43bf8f655b1c5a8276e3 Mon Sep 17 00:00:00 2001
From: Steve Gordon <sgordon@hotmail.co.uk>
Date: Tue, 30 Jan 2024 08:11:15 +0000
Subject: [PATCH] Fix serialisation of empty and single item `Fields` instances
 (#8018)

---
 .../Core/Infer/Fields/Fields.cs                  |  2 +-
 .../Core/Infer/Fields/FieldsConverter.cs         | 16 +++++++++++++++-
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/src/Elastic.Clients.Elasticsearch.Shared/Core/Infer/Fields/Fields.cs b/src/Elastic.Clients.Elasticsearch.Shared/Core/Infer/Fields/Fields.cs
index 840c6563ef6..debe5562826 100644
--- a/src/Elastic.Clients.Elasticsearch.Shared/Core/Infer/Fields/Fields.cs
+++ b/src/Elastic.Clients.Elasticsearch.Shared/Core/Infer/Fields/Fields.cs
@@ -27,7 +27,7 @@ public sealed class Fields : IUrlParameter, IEnumerable<Field>, IEquatable<Field
 
 	internal Fields() => ListOfFields = new List<Field>();
 
-	internal Fields(IEnumerable<Field> fieldNames) => ListOfFields = fieldNames.ToList();
+	internal Fields(IEnumerable<Field> fieldNames) => ListOfFields = new List<Field>(fieldNames);
 
 	private string DebugDisplay =>
 		$"Count: {ListOfFields.Count} [" +
diff --git a/src/Elastic.Clients.Elasticsearch.Shared/Core/Infer/Fields/FieldsConverter.cs b/src/Elastic.Clients.Elasticsearch.Shared/Core/Infer/Fields/FieldsConverter.cs
index 1788f8d1e1a..3c7b65ca352 100644
--- a/src/Elastic.Clients.Elasticsearch.Shared/Core/Infer/Fields/FieldsConverter.cs
+++ b/src/Elastic.Clients.Elasticsearch.Shared/Core/Infer/Fields/FieldsConverter.cs
@@ -22,7 +22,8 @@ internal sealed class FieldsConverter : JsonConverter<Fields>
 			Fields fields = reader.GetString();
 			return fields;
 		}
-		else if (reader.TokenType == JsonTokenType.StartArray)
+
+		if (reader.TokenType == JsonTokenType.StartArray)
 		{
 			var fields = new List<Field>();
 			while (reader.Read() && reader.TokenType != JsonTokenType.EndArray)
@@ -45,6 +46,19 @@ public override void Write(Utf8JsonWriter writer, Fields value, JsonSerializerOp
 			return;
 		}
 
+		if (value.ListOfFields.Count == 0)
+		{
+			writer.WriteStartObject();
+			writer.WriteEndObject();
+			return;
+		}
+
+		if (value.ListOfFields.Count == 1)
+		{
+			JsonSerializer.Serialize(writer, value.ListOfFields[0], options);
+			return;
+		}
+
 		writer.WriteStartArray();
 		foreach (var field in value.ListOfFields)
 		{