#vulnerable code 
                                private TokenExtractorResult matchDynamics(List<LexicalPatternElement> elements, TokenizedSource[] dynamics) {
        TokenExtractorResult result = new TokenExtractorResult(true);

        for (int i = 0; i < elements.size(); i++) {
            LexicalPatternElement nodeElement = elements.get(i);

            if (nodeElement.isUnit()) {
                continue;
            }

            if (dynamics.length == 0 && nodeElement.isOptional()) {
                continue;
            }

            TokenizedSource nodeContent = dynamics[i];
            dynamics[i] = null;

            if (nodeContent == null) {
                return new TokenExtractorResult();
            }

            TokenExtractorResult nodeElementResult = this.extract(nodeElement, new PandaTokenReader(nodeContent));

            if (!nodeElementResult.isMatched()) {
                return new TokenExtractorResult();
            }

            result.addIdentifier(nodeElement.getIdentifier());
            result.merge(nodeElementResult);
        }

        for (TokenizedSource dynamicContent : dynamics) {
            if (dynamicContent != null) {
                return new TokenExtractorResult(false);
            }
        }

        return result;
    } 
                            #location 24 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                private TokenExtractorResult matchDynamics(List<LexicalPatternElement> elements, TokenizedSource[] dynamics) {
        TokenExtractorResult result = new TokenExtractorResult(true);

        for (int i = 0; i < elements.size(); i++) {
            LexicalPatternElement nodeElement = elements.get(i);

            if (nodeElement.isUnit()) {
                continue;
            }

            if (dynamics.length == 0 && nodeElement.isOptional()) {
                continue;
            }

            TokenizedSource nodeContent = dynamics[i];
            dynamics[i] = null;

            if (nodeContent == null) {
                return new TokenExtractorResult();
            }

            TokenDistributor content = new TokenDistributor(nodeContent);
            TokenExtractorResult nodeElementResult = this.extract(nodeElement, content);

            if (!nodeElementResult.isMatched()) {
                return new TokenExtractorResult();
            }

            if (content.hasNext()) {
                int nextIndex = i + 1;

                if (nextIndex >= dynamics.length || dynamics[nextIndex] != null) {
                    return new TokenExtractorResult();
                }

                dynamics[nextIndex] = new PandaTokenizedSource(content.next(content.length() - content.getIndex()));
            }

            result.addIdentifier(nodeElement.getIdentifier());
            result.merge(nodeElementResult);
        }

        for (TokenizedSource dynamicContent : dynamics) {
            if (dynamicContent != null) {
                return new TokenExtractorResult();
            }
        }

        return result;
    }