log4net layout to write logs in JSON format

JsonLayout.cs

public class JsonLayout : LayoutSkeleton
{
    private class Container
    {
        public DateTime Timestamp { get; set; }
        public string Level { get; set; }
        public string Logger { get; set; }
        public object Message { get; set; }
        public string ThreadName { get; set; }
        public int ThreadId { get; set; }
        public string Domain { get; set; }
        public string Identity { get; set; }
        public string UserName { get; set; }
        public string Exception { get; set; }
        public Dictionary<string, object> Properties { get; set; }
        public LocationInfo LocationInfo { get; set; }
    }

    private string[] _properties = new string[] { "NDC" };

    public override bool IgnoresException
    {
        get
        {
            return base.IgnoresException;
        }

        set
        {
            base.IgnoresException = value;
        }
    }

    /// <summary>
    /// Gets or sets comma or semicolon delimited string that specifies which properties
    /// will be added to the properties of each log event.
    /// Properties looked up via loggingEvent.LookupProperty() method that covers
    /// inherited properties as well (Global, Thread contexts, etc).
    /// </summary>
    public string Properties { get; set; }

    public bool LocationInfo { get; set; }

    public JsonLayout()
    {
        // this layout will write exception itself, indicate it to appenders
        IgnoresException = false;
    }

    public override void ActivateOptions()
    {
        if (Properties != null)
            _properties = Properties.Split(',', ';').Select(x => x.Trim()).ToArray();
    }

    public override void Format(TextWriter writer, LoggingEvent loggingEvent)
    {
        var properties = new Dictionary<string, object>();

        foreach (var propName in loggingEvent.Properties.GetKeys())
            properties[propName] = loggingEvent.Properties[propName];

        foreach (var propName in _properties)
        {
            object propValue = loggingEvent.LookupProperty(propName);

            // special case for log4net internal property, it does not make sense to log it as object
            // as it will be like {Count: 1} w/o any string key at all
            if (propName == "NDC")
                propValue = propValue?.ToString();

            properties[propName] = propValue;
        }

        var data = new Container()
        {
            Timestamp        = loggingEvent.TimeStamp.ToUniversalTime(),
            ThreadName       = loggingEvent.ThreadName,
            ThreadId         = Thread.CurrentThread.ManagedThreadId,
            Level            = loggingEvent.Level.Name,
            Logger           = loggingEvent.LoggerName,
            Domain           = loggingEvent.Domain,
            Identity         = loggingEvent.Identity,
            UserName         = loggingEvent.UserName,
            Message          = loggingEvent.MessageObject,
            Exception        = loggingEvent.GetExceptionString(),
            Properties       = properties,
        };

        if (LocationInfo)
            data.LocationInfo = loggingEvent.LocationInformation;

        var json = JsonConvert.SerializeObject(data);

        writer.WriteLine(json);
    }
}