fix npte

src/main/java/com/chainself/service/GitlabMergeRequestService.java

@@ -57,6 +57,9 @@ public class GitlabMergeRequestService {
 		List<Long> mqidList = mqList.stream().map(GitlabMergeRequest::getId).collect(Collectors.toList());
 
 		List<Object[]> notes = gitlabMergeRequestDao.listNoteByMqid(mqidList);
+		if (notes.isEmpty()) {
+			return;
+		}
 		Map<Long, List<Object[]>> mapNotes = notes.stream().collect(Collectors.groupingBy(note -> {
 			return StringUtil.getNullLong(note[1]);
 		}));