output: #fixed code
                                  @Override
      public void makeBuildVariables(@SuppressWarnings("rawtypes") AbstractBuild build, Map<String,String> variables){
          variables.put("ghprbUpstreamStatus", "true");
          variables.put("ghprbCommitStatusContext", commitStatusContext);
          variables.put("ghprbTriggeredStatus", triggeredStatus);
          variables.put("ghprbStartedStatus", startedStatus);
          variables.put("ghprbStatusUrl", statusUrl);
          
          Map<GHCommitState, StringBuilder> statusMessages = new HashMap<GHCommitState, StringBuilder>(5);
          
          for (GhprbBuildResultMessage message : completedStatus) {
              GHCommitState state = message.getResult();
              StringBuilder sb;
              if (!statusMessages.containsKey(state)) {
                  sb = new StringBuilder();
                  statusMessages.put(state, sb);
              } else {
                  sb = statusMessages.get(state);
                  sb.append("\n");
              }
              sb.append(message.getMessage());
          }
          
          for (Entry<GHCommitState, StringBuilder> next : statusMessages.entrySet()) {
              String key = String.format("ghprb%sMessage", next.getKey().name());
              variables.put(key, next.getValue().toString());
          }
      }
input: #vulnerable code 
                                  @Override
      public void makeBuildVariables(@SuppressWarnings("rawtypes") AbstractBuild build, Map<String,String> variables){
          variables.put("ghprbUpstreamStatus", "true");
          variables.put("ghprbCommitStatusContext", commitStatusContext);
          variables.put("ghprbTriggeredStatus", triggeredStatus);
          variables.put("ghprbStartedStatus", startedStatus);
          variables.put("ghprbStatusUrl", statusUrl);
          
          Map<GHCommitState, StringBuilder> statusMessages = new HashMap<GHCommitState, StringBuilder>(5);
          
          for (GhprbBuildResultMessage message : completedStatus) {
              GHCommitState state = message.getResult();
              StringBuilder sb;
              if (statusMessages.containsKey(state)){
                  sb = new StringBuilder();
                  statusMessages.put(state, sb);
              } else {
                  sb = statusMessages.get(state);
                  sb.append("\n");
              }
              sb.append(message.getMessage());
          }
          
          for (Entry<GHCommitState, StringBuilder> next : statusMessages.entrySet()) {
              String key = String.format("ghprb%sMessage", next.getKey().name());
              variables.put(key, next.getValue().toString());
          }
      } 
                              #location 19 
                              #vulnerability type NULL_DEREFERENCE