What he is missing is that if the max. 3 pointer comparisons in (together with the function call of `Is`)

    if err == nil || target == nil {
        return err == target
    }

are a "pretty big performance penalty", there isn't much work going on. I mean, of course, these 2 or 3 comparisons + the function call of `Is` are at least double that of

      err != nil

even if `Is` would have been inlined by the compiler.