def stringify_keys(allowed: nil)
      allowed ||= self.class.allowed[:keys]
      each_with_object({}) do |(k, v), h|
        k = k.to_s unless allowed.include?(k.class)
        h[k] = !v.respond_to?(:stringify_keys) ? v : v.stringify_keys({
          :allowed => allowed
        })
      end
    end
def stringify_keys(allowed: nil)
      allowed ||= self.class.allowed[:keys]
      each_with_object({}) do |(k, v), h|
        k = k.to_s unless allowed.include?(k.class)
        h[k] = !v.respond_to?(:stringify_keys) ? v : v.stringify_keys({
          :allowed => allowed
        })
      end
    end
------------------------------------------------------------------------
 Stringify the keys of the current hash, skipping allowed objects.
 ------------------------------------------------------------------------