Program: 7823
Project: 7823
Buggy source:
public Object execute(final ExecutionEvent event) throws ExecutionException {
  RepositoryTreeNode node=getSelectedNodes(event).get(0);
  final Repository repository=node.getRepository();
  if (!canMerge(repository))   return null;
  String targetRef;
  if (node instanceof RefNode) {
    String refName=((RefNode)node).getObject().getName();
    try {
      if (repository.getFullBranch().equals(refName))       targetRef=null;
 else       targetRef=refName;
    }
 catch (    IOException e) {
      targetRef=null;
    }
  }
 else   if (node instanceof TagNode)   targetRef=((TagNode)node).getObject().getName();
 else   targetRef=null;
  final String refName;
  if (targetRef != null)   refName=targetRef;
 else {
    MergeTargetSelectionDialog mergeTargetSelectionDialog=new MergeTargetSelectionDialog(getShell(event),repository);
    if (mergeTargetSelectionDialog.open() == IDialogConstants.OK_ID) {
      refName=mergeTargetSelectionDialog.getRefName();
    }
 else {
      return null;
    }
  }
  String jobname=NLS.bind(UIText.MergeAction_JobNameMerge,refName);
  final MergeOperation op=new MergeOperation(repository,refName);
  Job job=new Job(jobname){
    @Override protected IStatus run(    IProgressMonitor monitor){
      try {
        op.execute(monitor);
      }
 catch (      final CoreException e) {
        return e.getStatus();
      }
      return Status.OK_STATUS;
    }
  }
;
  job.setUser(true);
  job.addJobChangeListener(new JobChangeAdapter(){
    @Override public void done(    IJobChangeEvent jobEvent){
      IStatus result=jobEvent.getJob().getResult();
      if (result.getSeverity() == IStatus.CANCEL) {
        Display.getDefault().asyncExec(new Runnable(){
          public void run(){
            try {
              MessageDialog.openInformation(getActiveShell(event),UIText.MergeAction_MergeCanceledTitle,UIText.MergeAction_MergeCanceledMessage);
            }
 catch (            ExecutionException e) {
              Activator.handleError(UIText.MergeAction_MergeCanceledMessage,null,true);
            }
          }
        }
);
      }
 else       if (!result.isOK()) {
        Activator.handleError(result.getMessage(),result.getException(),true);
      }
 else {
        Display.getDefault().asyncExec(new Runnable(){
          public void run(){
            try {
              MessageDialog.openInformation(getActiveShell(event),UIText.MergeAction_MergeResultTitle,op.getResult().toString());
            }
 catch (            ExecutionException e) {
              Activator.handleError(op.getResult().toString(),null,true);
            }
          }
        }
);
      }
    }
  }
);
  job.schedule();
  return null;
}

Fixed version (ground truth):
public Object execute(final ExecutionEvent event) throws ExecutionException {
  RepositoryTreeNode node=getSelectedNodes(event).get(0);
  final Repository repository=node.getRepository();
  if (!canMerge(repository))   return null;
  String targetRef;
  if (node instanceof RefNode) {
    String refName=((RefNode)node).getObject().getName();
    try {
      if (repository.getFullBranch().equals(refName))       targetRef=null;
 else       targetRef=refName;
    }
 catch (    IOException e) {
      targetRef=null;
    }
  }
 else   if (node instanceof TagNode)   targetRef=((TagNode)node).getObject().getName();
 else   targetRef=null;
  final String refName;
  if (targetRef != null)   refName=targetRef;
 else {
    MergeTargetSelectionDialog mergeTargetSelectionDialog=new MergeTargetSelectionDialog(getShell(event),repository);
    if (mergeTargetSelectionDialog.open() == IDialogConstants.OK_ID) {
      refName=mergeTargetSelectionDialog.getRefName();
    }
 else {
      return null;
    }
  }
  String jobname=NLS.bind(UIText.MergeAction_JobNameMerge,refName);
  final MergeOperation op=new MergeOperation(repository,refName);
  Job job=new Job(jobname){
    @Override protected IStatus run(    IProgressMonitor monitor){
      try {
        op.execute(monitor);
      }
 catch (      final CoreException e) {
        return e.getStatus();
      }
      return Status.OK_STATUS;
    }
  }
;
  job.setUser(true);
  job.setRule(op.getSchedulingRule());
  job.addJobChangeListener(new JobChangeAdapter(){
    @Override public void done(    IJobChangeEvent jobEvent){
      IStatus result=jobEvent.getJob().getResult();
      if (result.getSeverity() == IStatus.CANCEL) {
        Display.getDefault().asyncExec(new Runnable(){
          public void run(){
            Shell shell=PlatformUI.getWorkbench().getActiveWorkbenchWindow().getShell();
            MessageDialog.openInformation(shell,UIText.MergeAction_MergeCanceledTitle,UIText.MergeAction_MergeCanceledMessage);
          }
        }
);
      }
 else       if (!result.isOK()) {
        Activator.handleError(result.getMessage(),result.getException(),true);
      }
 else {
        Display.getDefault().asyncExec(new Runnable(){
          public void run(){
            Shell shell=PlatformUI.getWorkbench().getActiveWorkbenchWindow().getShell();
            MessageDialog.openInformation(shell,UIText.MergeAction_MergeResultTitle,op.getResult().toString());
          }
        }
);
      }
    }
  }
);
  job.schedule();
  return null;
}