The project in question is using React-16.2.0 which has the capability to use Fragments and the Fragment shorthand.
https://reactjs.org/blog/2017/11/28/react-v16.2.0
You can use the poor man's fragment shorthand as a quick fix: [ , ]
[
,
]
render(){ return [ foo, bar ] }
as array is totally a valid jsx element.