Set raster to NoData outside of Polygon

Let me preface as I know this topic has been addressed in various iterations, but between reviewing past FME Community Answers, the old Google Forum, and the Knowledge Base I am still having some difficulties.

 

 

Short of the long, I am converting a vector (polygon) dataset to raster. So far so good as the NumericRasterizer works perfectly. The problem I am running into is that I need to set the area outside of my Area of Interest polygon to NoData.

 

 

Ideal Scenario:

 

 

 

 

 

Here is part of the Workbench having the issue: 

 

 

 

 

I get the following error message: 

 

 

RasterMosaicker(RasterMosaicFactory): The band nodata value 'NULL' of the selected band '1:0' does not match the band nodata value '255' of the corresponding band in the mosaicked raster

 

 

Basically, how do I force the outside to be set as NoData and then mosaic back together with inside features so that when it's writen out as a GeoTIFF, the correct values of 5 & 0 are inside and outside the polygon is NoData.

 

 

Thanks in advance,

 

 

 

 

Matt