this(out, null);
    }

    public SystemLogger(@Nullable OutputStream out, @Nullable Level threshold) {
        this.out = new PrintWriter(toPsOrDef(out, System.err), true);
        this.threshold = Objects.requireNonNullElse(threshold, Level.INFO);
    }

    private PrintStream toPsOrDef(OutputStream outputStream, PrintStream def) {
        if (outputStream == null) {
            return def;
        }