Implement IRawValue on ${whenEmpty}

[304NotModified]

fixes #3372

related: #3373 and #3139

[304NotModified]

@snakefoot could you please help me getting this ready?

I doesn't work unfortunately, probably because MutableUnsafe = true. See this screenie when debugging (SimpleLayout.cs)

Any idea how to fix that?

Also think this isn't the most efficient way, but dunno how to write a more efficient test.

   public bool TryGetRawValue(LogEventInfo logEvent, out object value)
        {
            var item = Inner.Render(logEvent);
            if (item.Length > 0)
                 ...

       }

[snakefoot]

Don't do this:

var item = Inner.Render(logEvent);

Instead check if the raw-value-returned is null or empty-string.

[snakefoot]

Created #3398

[304NotModified]

Syoer