output: #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));
      }
input: #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