Processor 'FontDescriptionProcessor' had an unexpected failure. Null Reference Exception (TTF Font)

I have a truetype font file i’m trying to import into monogame. Following the documentation I added a new
.spritefont and then edited that .spritefont to have the postscript name of my truetype font

<FontName>MyTrueTypeFont</FontName> I also did this with .ttf at the end
My Importer is sprite font importer and processor is sprite font description.
Although whenever i try to build it gives me the error in the title.

I’m trying to build the .spritefont file in the pipeline content tool to make it an .xnb