Program: 62687
Project: 62687
Buggy source:
public void onPost(final GitLabMergeRequest req){
  if (triggerOnMergeRequest) {
    getDescriptor().queue.execute(new Runnable(){
      public void run(){
        LOGGER.log(Level.INFO,"String_Node_Str",job.getName());
        String name="String_Node_Str" + job.getNextBuildNumber();
        GitLabMergeCause cause=createGitLabMergeCause(req);
        Action[] actions=createActions(req);
        setBuildCauseInJob(req);
        if (job.scheduleBuild(job.getQuietPeriod(),cause,actions)) {
          LOGGER.log(Level.INFO,"String_Node_Str",new String[]{job.getName(),name});
        }
 else {
          LOGGER.log(Level.INFO,"String_Node_Str",job.getName());
        }
      }
      private GitLabMergeCause createGitLabMergeCause(      GitLabMergeRequest req){
        GitLabMergeCause cause;
        try {
          cause=new GitLabMergeCause(req,getLogFile());
        }
 catch (        IOException ex) {
          cause=new GitLabMergeCause(req);
        }
        return cause;
      }
      private Action[] createActions(      GitLabMergeRequest req){
        List<Action> actions=new ArrayList<Action>();
        Map<String,ParameterValue> values=new HashMap<String,ParameterValue>();
        values.put("String_Node_Str",new StringParameterValue("String_Node_Str",getSourceBranch(req)));
        values.put("String_Node_Str",new StringParameterValue("String_Node_Str",req.getObjectAttribute().getTargetBranch()));
        String sourceRepoName=getDesc().getSourceRepoNameDefault();
        String sourceRepoURL=getDesc().getSourceRepoURLDefault().toString();
        if (!getDescriptor().getGitlabHostUrl().isEmpty()) {
          try {
            sourceRepoName=req.getSourceProject(getDesc().getGitlab()).getPathWithNamespace();
            sourceRepoURL=req.getSourceProject(getDesc().getGitlab()).getSshUrl();
          }
 catch (          IOException ex) {
            LOGGER.log(Level.WARNING,"String_Node_Str",new String[]{ex.toString(),ex.getMessage()});
          }
        }
        values.put("String_Node_Str",new StringParameterValue("String_Node_Str",sourceRepoName));
        values.put("String_Node_Str",new StringParameterValue("String_Node_Str",sourceRepoURL));
        List<ParameterValue> listValues=new ArrayList<ParameterValue>(values.values());
        ParametersAction parametersAction=new ParametersAction(listValues);
        actions.add(parametersAction);
        Action[] actionsArray=actions.toArray(new Action[0]);
        return actionsArray;
      }
    }
);
  }
}

Fixed version (ground truth):
public void onPost(final GitLabMergeRequest req){
  if (triggerOnMergeRequest) {
    getDescriptor().queue.execute(new Runnable(){
      public void run(){
        LOGGER.log(Level.INFO,"String_Node_Str",job.getName());
        String name="String_Node_Str" + job.getNextBuildNumber();
        GitLabMergeCause cause=createGitLabMergeCause(req);
        Action[] actions=createActions(req);
        if (job.scheduleBuild(job.getQuietPeriod(),cause,actions)) {
          LOGGER.log(Level.INFO,"String_Node_Str",new String[]{job.getName(),name});
        }
 else {
          LOGGER.log(Level.INFO,"String_Node_Str",job.getName());
        }
      }
      private GitLabMergeCause createGitLabMergeCause(      GitLabMergeRequest req){
        GitLabMergeCause cause;
        try {
          cause=new GitLabMergeCause(req,getLogFile());
        }
 catch (        IOException ex) {
          cause=new GitLabMergeCause(req);
        }
        return cause;
      }
      private Action[] createActions(      GitLabMergeRequest req){
        List<Action> actions=new ArrayList<Action>();
        Map<String,ParameterValue> values=new HashMap<String,ParameterValue>();
        values.put("String_Node_Str",new StringParameterValue("String_Node_Str",getSourceBranch(req)));
        values.put("String_Node_Str",new StringParameterValue("String_Node_Str",req.getObjectAttribute().getTargetBranch()));
        String sourceRepoName=getDesc().getSourceRepoNameDefault();
        String sourceRepoURL=getDesc().getSourceRepoURLDefault().toString();
        if (!getDescriptor().getGitlabHostUrl().isEmpty()) {
          try {
            sourceRepoName=req.getSourceProject(getDesc().getGitlab()).getPathWithNamespace();
            sourceRepoURL=req.getSourceProject(getDesc().getGitlab()).getSshUrl();
          }
 catch (          IOException ex) {
            LOGGER.log(Level.WARNING,"String_Node_Str",new String[]{ex.toString(),ex.getMessage()});
          }
        }
        values.put("String_Node_Str",new StringParameterValue("String_Node_Str",sourceRepoName));
        values.put("String_Node_Str",new StringParameterValue("String_Node_Str",sourceRepoURL));
        List<ParameterValue> listValues=new ArrayList<ParameterValue>(values.values());
        ParametersAction parametersAction=new ParametersAction(listValues);
        actions.add(parametersAction);
        Action[] actionsArray=actions.toArray(new Action[0]);
        return actionsArray;
      }
    }
);
  }
}