fails:UnboundMethod#arity returns the number of arguments accepted by a method, using Method#unbind
fails:UnboundMethod#arity returns the number arguments accepted by a method, using Module#instance_method
fails:UnboundMethod#arity if optional arguments returns the negative number of mandatory arguments, using Method#unbind
fails:UnboundMethod#arity if optional arguments returns the negative number of mandatory arguments, using Module#instance_method
