fix merging collection

src/main/java/ru/ulstu/timeline/service/EventService.java

@@ -105,7 +105,7 @@ public class EventService {
     public void createFromPaper(Paper newPaper) {
         List<Timeline> timelines = timelineService.findAll();
         Timeline timeline = timelines.isEmpty() ? new Timeline() : timelines.get(0);
-
+        timeline.getEvents().removeAll(newPaper.getEvents());
         for (Deadline deadline : newPaper.getDeadlines()
                 .stream()
                 .filter(d -> d.getDate().after(new Date()) || DateUtils.isSameDay(d.getDate(), new Date()))
@@ -119,16 +119,13 @@ public class EventService {
             newEvent.setDescription("Дедлайн '" + deadline.getDescription() + "' cтатьи '" + newPaper.getTitle() + "'");
             newEvent.setRecipients(new ArrayList(newPaper.getAuthors()));
             newEvent.setPaper(newPaper);
-            eventRepository.save(newEvent);
-
-            timeline.getEvents().add(newEvent);
-            timelineService.save(timeline);
+            timeline.getEvents().add(eventRepository.save(newEvent));
         }
+        timelineService.save(timeline);
     }
 
     public void updatePaperDeadlines(Paper paper) {
         eventRepository.delete(eventRepository.findAllByPaper(paper));
-
         createFromPaper(paper);
     }