#vulnerable code 
                                public void transactionObject(final String trytes) {

        if (StringUtils.isEmpty(trytes)) {
            log.warn("Warning: empty trytes in input for transactionObject");
            return;
        }

        // validity check
        for (int i = 2279; i < 2295; i++) {
            if (trytes.charAt(i) != '9') {
                log.warn("Trytes {} does not seem a valid tryte", trytes);
                return;
            }
        }

        int[] transactionTrits = Converter.trits(trytes);
        int[] hash = new int[243];

        ICurl curl = SpongeFactory.create(SpongeFactory.Mode.CURL);
        // generate the correct transaction hash
        curl.reset();
        curl.absorb(transactionTrits, 0, transactionTrits.length);
        curl.squeeze(hash, 0, hash.length);

        this.setHash(Converter.trytes(hash));
        this.setSignatureFragments(trytes.substring(0, 2187));
        this.setAddress(trytes.substring(2187, 2268));
        this.setValue(Converter.longValue(Arrays.copyOfRange(transactionTrits, 6804, 6837)));
        this.setTag(trytes.substring(2295, 2322));
        this.setTimestamp(Converter.longValue(Arrays.copyOfRange(transactionTrits, 6966, 6993)));
        this.setCurrentIndex(Converter.longValue(Arrays.copyOfRange(transactionTrits, 6993, 7020)));
        this.setLastIndex(Converter.longValue(Arrays.copyOfRange(transactionTrits, 7020, 7047)));
        this.setBundle(trytes.substring(2349, 2430));
        this.setTrunkTransaction(trytes.substring(2430, 2511));
        this.setBranchTransaction(trytes.substring(2511, 2592));
        this.setNonce(trytes.substring(2592, 2673));
    } 
                            #location 21 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                public void transactionObject(final String trytes) {

        if (StringUtils.isEmpty(trytes)) {
            log.warn("Warning: empty trytes in input for transactionObject");
            return;
        }

        // validity check
        for (int i = 2279; i < 2295; i++) {
            if (trytes.charAt(i) != '9') {
                log.warn("Trytes {} does not seem a valid tryte", trytes);
                return;
            }
        }

        int[] transactionTrits = Converter.trits(trytes);
        int[] hash = new int[243];

        ICurl curl = SpongeFactory.create(SpongeFactory.Mode.CURLP81);
        // generate the correct transaction hash
        curl.reset();
        curl.absorb(transactionTrits, 0, transactionTrits.length);
        curl.squeeze(hash, 0, hash.length);

        this.setHash(Converter.trytes(hash));
        this.setSignatureFragments(trytes.substring(0, 2187));
        this.setAddress(trytes.substring(2187, 2268));
        this.setValue(Converter.longValue(Arrays.copyOfRange(transactionTrits, 6804, 6837)));
        this.setObsoleteTag(trytes.substring(2295, 2322));
        this.setTimestamp(Converter.longValue(Arrays.copyOfRange(transactionTrits, 6966, 6993)));
        this.setCurrentIndex(Converter.longValue(Arrays.copyOfRange(transactionTrits, 6993, 7020)));
        this.setLastIndex(Converter.longValue(Arrays.copyOfRange(transactionTrits, 7020, 7047)));
        this.setBundle(trytes.substring(2349, 2430));
        this.setTrunkTransaction(trytes.substring(2430, 2511));
        this.setBranchTransaction(trytes.substring(2511, 2592));
        this.setTag(trytes.substring(2592, 2619));
        this.setAttachmentTimestamp(Converter.longValue(Arrays.copyOfRange(transactionTrits, 7857, 7884)) / 1000);
        this.setAttachmentTimestampLowerBound(Converter.longValue(Arrays.copyOfRange(transactionTrits, 7884, 7911)));
        this.setAttachmentTimestampUpperBound(Converter.longValue(Arrays.copyOfRange(transactionTrits, 7911, 7938)));
        this.setNonce(trytes.substring(2646, 2673));
    }