private function getIndentAt(Tokens $tokens, $index)
    {
        if (1 === Preg::match('/\R{1}([ \t]*)$/', $this->getIndentContentAt($tokens, $index), $matches)) {
            return $matches[1];
        }

        return null;
    }
private function getIndentAt(Tokens $tokens, $index)
    {
        if (1 === Preg::match('/\R{1}([ \t]*)$/', $this->getIndentContentAt($tokens, $index), $matches)) {
            return $matches[1];
        }

        return null;
    }
@param Tokens $tokens
@param int    $index  index of the indentation token

@return null|string