code: func WrapErrf(cause error, format string, args ...interface{}) error {
  	if cause == nil {
  		return nil
  	}
  
  	err := cause.(*Err)
  	return &Err{
  		Code:    err.Code,
  		Message: fmt.Sprintf(format, args...),
  		Cause:   err,
  	}
  }
docs: /*
  WrapErrf returns an *Err that wraps another *Err and has the same ErrCode.
  Panics if cause is not an *Err.
  
  To wrap generic errors, use WrapErrorf.
  */