/Users/italoborges/.rvm/gems/ruby-1.9.3-p392/gems/activemodel-3.2.12/lib/active_model/validations/format.rb:17:in `check_validity!': Either :with or :without must be supplied (but not both) (ArgumentError)
from /Users/italoborges/.rvm/gems/ruby-1.9.3-p392/gems/activemodel-3.2.12/lib/active_model/validator.rb:143:in `initialize'
from /Users/italoborges/.rvm/gems/ruby-1.9.3-p392/gems/activemodel-3.2.12/lib/active_model/validations/with.rb:82:in `new'
from /Users/italoborges/.rvm/gems/ruby-1.9.3-p392/gems/activemodel-3.2.12/lib/active_model/validations/with.rb:82:in `block in validates_with'
from /Users/italoborges/.rvm/gems/ruby-1.9.3-p392/gems/activemodel-3.2.12/lib/active_model/validations/with.rb:81:in `each'
from /Users/italoborges/.rvm/gems/ruby-1.9.3-p392/gems/activemodel-3.2.12/lib/active_model/validations/with.rb:81:in `validates_with'