fix submit form

src/main/java/ru/ulstu/paper/controller/PaperController.java

@@ -48,6 +48,10 @@ public class PaperController {
 
     @PostMapping(value = "/paper", params = "save")
     public String save(@Valid PaperDto paperDto, Errors errors) throws IOException {
+        filterEmptyDeadlines(paperDto);
+        if (paperDto.getDeadlines().isEmpty()) {
+            errors.rejectValue("deadlines", "errorCode","Не может быть пустым");
+        }
         if (errors.hasErrors()) {
             return "/papers/paper";
         }

src/main/java/ru/ulstu/paper/model/Paper.java

@@ -158,6 +158,7 @@ public class Paper extends BaseEntity implements UserContainer {
     public Optional<Deadline> getNextDeadline() {
         return deadlines
                 .stream()
+                .filter(deadline -> deadline.getDate() != null)
                 .sorted(Comparator.comparing(Deadline::getDate))
                 .filter(d -> d.getDate().after(new Date()))
                 .findFirst();

src/main/java/ru/ulstu/paper/model/PaperDto.java

@@ -6,6 +6,7 @@ import org.hibernate.validator.constraints.NotEmpty;
 import ru.ulstu.deadline.model.DeadlineDto;
 
 import javax.validation.constraints.Size;
+import java.util.ArrayList;
 import java.util.Date;
 import java.util.List;
 import java.util.Set;
@@ -21,7 +22,7 @@ public class PaperDto {
     private Date createDate;
     private Date updateDate;
     @NotEmpty
-    private List<DeadlineDto> deadlines;
+    private List<DeadlineDto> deadlines = new ArrayList<>();
     private String comment;
     private Boolean locked;
     private String tmpFileName;
@@ -31,7 +32,7 @@ public class PaperDto {
     private Set<Integer> authors;
 
     public PaperDto() {
-
+        deadlines.add(new DeadlineDto());
     }
 
     @JsonCreator