You can filter the warnings by overriding Warning.warn, or using the warning gem:
require 'warning'
Warning.ignore(/`(els)?if' at the end of line without an expression/)
That's pretty cool! I did not know that was possible in quite that way. Learned
something there. :D
[Removed stuff here.]
Edit: Aaah yikes ... I misread your comment; you referred to the warning gem. I
thought this was part of ruby as-is. Well, still cool that this exists at the
least.