fixbugs

stmms-web/src/main/java/cn/com/qmth/stmms/api/controller/ExamStudentController.java

@@ -334,6 +334,9 @@ public class ExamStudentController extends BaseApiController {
         List<String> markerNames = new LinkedList<>();
         List<MarkLibrary> list = libraryService.findByStudentAndGroup(student.getId(), groupNumber);
         for (MarkLibrary library : list) {
+            if (library.getMarkerId() == null) {
+                continue;
+            }
             Marker marker = markerService.findById(library.getMarkerId());
             if (marker != null) {
                 markerNames.add(marker.getName());