How do I fix this annoying syntastic rails error
If all you want is not to see these messages again:
let g:syntastic_eruby_ruby_quiet_messages = \ {'regex': 'possibly useless use of a variable in void context'}
If there is a posibility that the warning will help in the future, the best thing to do is add .to_s to the msg so it makes the warning go away but you don't filter future warnings.