code: func IgnorableError(s string, args ...interface{}) ignorableError {
  	return ignorableError(fmt.Sprintf(s, args...))
  }
docs: // IgnorableError returns an error that we shouldn't handle (i.e. log) because
  // it's spammy and usually user error. Instead we will log these errors at a
  // higher log level. We still need to throw these errors to signal that the
  // sync should be retried.