class Bullet::Rack

def empty?(response)

fix issue if response's body is a Proc 
def empty?(response)
  # response may be ["Not Found"], ["Move Permanently"], etc, but
  # those should not happen if the status is 200
  return true if !response.respond_to?(:body) && !response.respond_to?(:first)
  body = response_body(response)
  body.nil? || body.empty?
end