Using Umbraco notifications with a Block List Editor

BlockListNotification.cs

using Umbraco.Cms.Core.Events;
using Umbraco.Cms.Core.Models.Blocks;
using Umbraco.Cms.Core.Notifications;

namespace Concept.Core.NotificationHandlers
{
    public class ContentPublishing : INotificationHandler<ContentPublishingNotification>
    {
        public void Handle(ContentPublishingNotification notification)
        {
            foreach (var node in notification.PublishedEntities)
            {
                var publishingCultures = node
                    .AvailableCultures
                    .Where(culture => notification.IsPublishingCulture(node, culture)).ToList();
                        
                var unPublishingCultures = node
                    .AvailableCultures
                    .Where(culture => notification.IsUnpublishingCulture(node, culture)).ToList();

                if (node.ContentType.Alias.Equals("standardPage"))
                {
                    foreach (var publishedCulture in publishingCultures)
                    {
                        var rawJson = node.GetValue("blocks", publishedCulture)?.ToString();

                        if (string.IsNullOrWhiteSpace(rawJson)) continue;

                        var blockValue = Newtonsoft.Json.JsonConvert.DeserializeObject<BlockValue>(rawJson);

                        if (blockValue is null) continue;

                        foreach (var item in blockValue.SettingsData)
                        {
                            foreach (var itemProperty in item.RawPropertyValues)
                            {
                                ...
                            }
                        }

                        foreach (var item in blockValue.ContentData)
                        {
                            foreach (var itemProperty in item.RawPropertyValues)
                            {
                                if (itemProperty.Key == "showWarning")
                                {
                                    notification.CancelOperation(new EventMessage("Warning", "Invalid configuration", EventMessageType.Error));
                                }
                            }     
                        }
                    }
                }
            }
        }
    }
}