private function parseNamespace($tokens)
    {
        $namespace = null;
        $tokenCount = count($tokens);
        for ($offset=0; $offset < $tokenCount; $offset++) {
            if (!is_array($tokens[$offset])) {
                continue;
            }

            if (T_NAMESPACE === $tokens[$offset][0]) {
                $offset++; // the next token is a whitespace

                return $this->parseNamespaceString($tokens, $offset);
            }
        }

        return $namespace;
    }