getImageTags Both err and tags are null

[AnthoniG]

I am trying to get this working but having no success.
Am on linux mint 18 and I've installed the exiv dependencies like it suggested.

Then I npm installed it and did the example on the front page

const ex = require('exiv2');

console.log('Library ', ex);

ex.getImageTags('./photo.png', function(err, tags) {
  if(err) {
    console.error('Error Reading Image', err);
    return;
  }
  
  if(!tags) {
    console.error('Tags was null');
    return;
  }
  
  console.log("DateTime: " + tags["Exif.Image.DateTime"]);
  console.log("DateTimeOriginal: " + tags["Exif.Photo.DateTimeOriginal"]);
});

However when I look into the function, both err and tags are not defined. Anyone have a clue what's going on please ?