protected override void Append(StringBuilder builder, LogEventInfo logEvent)
        {
            if (LogContext.Contains(Key) == false)
            {
                return;
            }

            var value = LogContext.Get <object>(Key);

            if (value is string && string.IsNullOrEmpty(Format))
            {
                builder.Append(value);
                return;
            }

            var formatProvider = logEvent.FormatProvider;

            if (Format == "@")
            {
                ConfigurationItemFactory.Default.ValueFormatter.FormatValue(value, null, CaptureType.Serialize, formatProvider, builder);
                return;
            }

            if (value == null)
            {
                return;
            }

            ConfigurationItemFactory.Default.ValueFormatter.FormatValue(value, Format, CaptureType.Normal, formatProvider, builder);
        }