fix: correct ReleaseNotes deserialization for AutoUpdater (fixes #1039)

src/ElectronNET.API/API/Entities/UpdateInfo.cs

@@ -1,4 +1,8 @@
-namespace ElectronNET.API.Entities
+using System;
+using System.Text.Json.Serialization;
+using ElectronNET.API.Converter;
+
+namespace ElectronNET.API.Entities
 {
     /// <summary>
     /// 
@@ -24,7 +28,8 @@ public class UpdateInfo
         /// <summary>
         /// Gets or sets the release notes.
         /// </summary>
-        public ReleaseNoteInfo[] ReleaseNotes { get; set; } = new ReleaseNoteInfo[0];
+        [JsonConverter(typeof(ReleaseNotesConverter))]
+        public ReleaseNoteInfo[] ReleaseNotes { get; set; } = Array.Empty<ReleaseNoteInfo>();
 
         /// <summary>
         /// Gets or sets the release date.

src/ElectronNET.API/Converter/ReleaseNotesConverter.cs

@@ -0,0 +1,91 @@
+using ElectronNET.API.Entities;
+using System;
+using System.Collections.Generic;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace ElectronNET.API.Converter;
+
+/// <summary>
+/// Handles the polymorphic shape of releaseNotes coming from electron-builder.
+/// Depending on the updater.fullChangelog setting, electron-builder sends:
+///   - null                        → when there are no notes
+///   - "some string"               → plain string (FullChangelog = false, default)
+///   - ["note A", "note B"]        → array of strings (after broken normalize in older TS)
+///   - [{ version, note }, ...]    → array of objects (FullChangelog = true)
+/// All forms are normalised to ReleaseNoteInfo[] so the C# model stays clean.
+/// See: https://github.com/ElectronNET/Electron.NET/issues/1039
+/// </summary>
+public class ReleaseNotesConverter : JsonConverter<ReleaseNoteInfo[]>
+{
+    // Ensure the converter is called even when the JSON token is null,
+    // so we can return an empty array instead of null.
+    public override bool HandleNull => true;
+
+    public override ReleaseNoteInfo[] Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+    {
+        switch (reader.TokenType)
+        {
+            case JsonTokenType.Null:
+                return Array.Empty<ReleaseNoteInfo>();
+
+            case JsonTokenType.String:
+                // Plain string: "Some release notes"
+                return new[] { new ReleaseNoteInfo { Note = reader.GetString() } };
+
+            case JsonTokenType.StartArray:
+                var list = new List<ReleaseNoteInfo>();
+                while (reader.Read() && reader.TokenType != JsonTokenType.EndArray)
+                {
+                    if (reader.TokenType == JsonTokenType.String)
+                    {
+                        // Array of strings: ["Note A", "Note B"]
+                        list.Add(new ReleaseNoteInfo { Note = reader.GetString() });
+                    }
+                    else if (reader.TokenType == JsonTokenType.StartObject)
+                    {
+                        // Array of objects: [{ "version": "1.0", "note": "..." }]
+                        var entry = JsonSerializer.Deserialize<ReleaseNoteInfo>(ref reader, options) ?? new ReleaseNoteInfo();
+                        list.Add(entry);
+                    }
+                    else
+                    {
+                        reader.Skip();
+                    }
+                }
+                return list.ToArray();
+
+            default:
+                throw new JsonException($"Unexpected token {reader.TokenType} when reading releaseNotes.");
+        }
+    }
+
+    public override void Write(Utf8JsonWriter writer, ReleaseNoteInfo[] value, JsonSerializerOptions options)
+    {
+        if (value is null)
+        {
+            writer.WriteNullValue();
+            return;
+        }
+
+        if (value.Length == 0)
+        {
+            writer.WriteStartArray();
+            writer.WriteEndArray();
+            return;
+        }
+
+        writer.WriteStartArray();
+        foreach (var item in value)
+        {
+            writer.WriteStartObject();
+            if (item.Version is not null)
+            {
+                writer.WriteString("version", item.Version);
+            }
+            writer.WriteString("note", item.Note);
+            writer.WriteEndObject();
+        }
+        writer.WriteEndArray();
+    }
+}

src/ElectronNET.Host/api/autoUpdater.ts

@@ -5,7 +5,11 @@ let electronSocket: Socket;
 
 function normalize(updateInfo) {
   if (typeof updateInfo?.releaseNotes === "string") {
-    updateInfo.releaseNotes = [updateInfo.releaseNotes];
+    updateInfo.releaseNotes = [{ note: updateInfo.releaseNotes }];
+  } else if (Array.isArray(updateInfo?.releaseNotes)) {
+    updateInfo.releaseNotes = updateInfo.releaseNotes.map((entry) =>
+      typeof entry === "string" ? { note: entry } : entry,
+    );
   }
 }