Component Exception Can't find variable: user

[larguelles]

After completing every step I get an the error mentioned in the title when trying to navigate to the HomeScreen:
On line 50 of App.js: {props => <HomeScreen {...props} extraData={user} />}
I've even tried copying and pasting every line of the source code on the repo rather than following the steps on the tutorial to see if it was some sort of typing mistake on my behalf but have found no fix to this.
Any ideas?