ofxGeoJSON problem parsing json files

Openframeworks has an ofxGeoJSON addon for importing and rendering json files. However, I can’t get the addon to visualise files other than the one in the addon directory.

I have a json file that I would like visualised and have checked its format using an online format corrector ( https://jsonformatter.curiousconcept.com ) which will format json into the compact version. Running the file in Openframeworks using ofxGeoJSON creates the message:

'parsingSuccessful to parse JSON
[notice ] index: 0 null

[notice ] Succeed to load geojson…’

But the map is not rendered. I’m not sure what ‘index: 0 null’ means. Is this a json file format issue? Thanks for your assistance.