From d2dc8e047dd12ad9fb531045d5a1ef63a916329b Mon Sep 17 00:00:00 2001
From: Andy Butland <abutland73@gmail.com>
Date: Mon, 16 Jun 2025 22:01:24 +0200
Subject: [PATCH] Further fix to configuration classes using ISet, resolving
 regression with custom 404 pages.

---
 src/Umbraco.Core/CompatibilitySuppressions.xml        | 11 +++++++++++
 .../Configuration/Models/ContentSettings.cs           |  2 +-
 .../Validation/ContentSettingsValidatorTests.cs       |  4 ++--
 3 files changed, 14 insertions(+), 3 deletions(-)
 create mode 100644 src/Umbraco.Core/CompatibilitySuppressions.xml

diff --git a/src/Umbraco.Core/CompatibilitySuppressions.xml b/src/Umbraco.Core/CompatibilitySuppressions.xml
new file mode 100644
index 000000000000..3cd59acc387e
--- /dev/null
+++ b/src/Umbraco.Core/CompatibilitySuppressions.xml
@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- https://learn.microsoft.com/dotnet/fundamentals/package-validation/diagnostic-ids -->
+<Suppressions xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
+  <Suppression>
+    <DiagnosticId>CP0002</DiagnosticId>
+    <Target>M:Umbraco.Cms.Core.Configuration.Models.ContentSettings.get_Error404Collection</Target>
+    <Left>lib/net9.0/Umbraco.Core.dll</Left>
+    <Right>lib/net9.0/Umbraco.Core.dll</Right>
+    <IsBaselineSuppression>true</IsBaselineSuppression>
+  </Suppression>
+</Suppressions>
\ No newline at end of file
diff --git a/src/Umbraco.Core/Configuration/Models/ContentSettings.cs b/src/Umbraco.Core/Configuration/Models/ContentSettings.cs
index 3e89369f000d..6df9b429e907 100644
--- a/src/Umbraco.Core/Configuration/Models/ContentSettings.cs
+++ b/src/Umbraco.Core/Configuration/Models/ContentSettings.cs
@@ -50,7 +50,7 @@ public class ContentSettings
     /// <summary>
     ///     Gets or sets a value for the collection of error pages.
     /// </summary>
-    public ISet<ContentErrorPage> Error404Collection { get; set; } = new HashSet<ContentErrorPage>();
+    public IEnumerable<ContentErrorPage> Error404Collection { get; set; } = [];
 
     /// <summary>
     ///     Gets or sets a value for the preview badge mark-up.
diff --git a/tests/Umbraco.Tests.UnitTests/Umbraco.Core/Configuration/Models/Validation/ContentSettingsValidatorTests.cs b/tests/Umbraco.Tests.UnitTests/Umbraco.Core/Configuration/Models/Validation/ContentSettingsValidatorTests.cs
index bea57e67863e..1d4afe2c3bc1 100644
--- a/tests/Umbraco.Tests.UnitTests/Umbraco.Core/Configuration/Models/Validation/ContentSettingsValidatorTests.cs
+++ b/tests/Umbraco.Tests.UnitTests/Umbraco.Core/Configuration/Models/Validation/ContentSettingsValidatorTests.cs
@@ -42,9 +42,9 @@ private static ContentSettings BuildContentSettings(string culture = "en-US", st
             new ContentSettings
             {
                 Error404Collection =
-                {
+                [
                     new() { Culture = culture, ContentId = 1 },
-                },
+                ],
                 Imaging =
                 {
                     AutoFillImageProperties =