__examples__/symbols example not working?

Have been trying to see how to generate an artboard which has symbols on it so referred to this example to try and get something working. Not sure if this is a Sketch version issue, but generating a sketch file from this example fails to open in Sketch. The Sketch version I'm trying to open in is Version 68 (102490).

Opening the file in sketch results in an error: 'the document could not be opened'

commenting the following line in symbols/index.js:
```
// page.addArtboard(symbol);
```
and regenerating the sketch file results in the Sketch file opening fine, but obviously the link to the symbol is broken.

just wondering which part is breaking, have been trying to reverse engineer this using Kactus to see what a correct SymbolMaster.json looks like but am still scratching my head at this stage. Wondering if others have come across this issue.

Start with __examples__/symbols/index.js and reproduce the generated Sketch file in Sketch Version 68. Focus on the page.addArtboard(symbol) call and determine why including it makes the document fail to open; done means the generated file opens while retaining the symbol link.

Written by the indexing model from the issue text.