#fixed code
                                public boolean extract(TokenizedSource tokenizedSource) {
        TokenPatternUnit[] units = pattern.getUnits();
        ArrayDistributor<TokenPatternUnit> unitsDistributor = new ArrayDistributor<>(units);

        TokenReader tokenReader = new PandaTokenReader(tokenizedSource);
        TokenHollow hollow = new TokenHollow();

        for (int unitIndex = 0; unitIndex < units.length; unitIndex++) {
            TokenPatternUnit unit = unitsDistributor.get(unitIndex);
            tokenReader.synchronize();

            for (TokenRepresentation representation : tokenReader) {
                Token token = representation.getToken();

                if (unit.equals(token)) {
                    tokenReader.read();
                    break;
                }

                if (!unit.isHollow()) {
                    return false;
                }

                TokenPatternUnit nextUnit = unitsDistributor.get(unitIndex + 1);

                if (!token.equals(nextUnit) || extractorOpposites.isLocked()) {
                    extractorOpposites.report(token);

                    tokenReader.read();
                    hollow.addToken(token);

                    continue;
                }

                hollows.add(hollow);
                hollow = new TokenHollow();
                break;
            }
        }

        return tokenReader.getIndex() + 1 >= tokenizedSource.size();
    }
#vulnerable code 
                                public boolean extract(TokenizedSource tokenizedSource) {
        TokenPatternUnit[] units = pattern.getUnits();
        ArrayDistributor<TokenPatternUnit> unitsDistributor = new ArrayDistributor<>(units);

        TokenReader tokenReader = new PandaTokenReader(tokenizedSource);
        Stack<Separator> separators = new Stack<>();

        for (int unitIndex = 0; unitIndex < units.length; unitIndex++) {
            TokenPatternUnit unit = unitsDistributor.get(unitIndex);
            TokenPatternUnit nextUnit = unitsDistributor.get(unitIndex + 1);

            loop:
            if (!unit.isHollow()) {

            }
            else {

            }
        }

        return tokenReader.getIndex() >= tokenizedSource.size();
    } 
                            #location 13 
                            #vulnerability type NULL_DEREFERENCE