Typo in error message "does not exists"

I've fixed the 'not exists' typo and also added 'the' as a prefix to 'filesystem' to improve readability.

Thanks for the fix @nicrodgers!

@nicrodgers could you rebase you MR so I can merge it please?

Thanks @nicrodgers, it's merged.

Automatically closed - issue fixed for 2 weeks with no activity.