public function withIsoNumeric(string $isoNumeric = null): self
    {
        $new = clone $this;
        $new->isoNumeric = null === $isoNumeric ? null : (int) $isoNumeric;

        return $new;
    }
public function withIsoNumeric(string $isoNumeric = null): self
    {
        $new = clone $this;
        $new->isoNumeric = null === $isoNumeric ? null : (int) $isoNumeric;

        return $new;
    }
@param string|null $isoNumeric

@return CountryInfo