Merge branch '303-manager-cannot-update-student-assistant' into 'development'

Resolve "Manager cannot update student/assistant"

Closes #303

See merge request !385

src/main/java/nl/tudelft/ewi/queue/service/PermissionService.java

@@ -102,14 +102,14 @@ public class PermissionService {
 
 	public boolean canUpdateParticipant(Object principal, Long courseId, Long participantId) {
 		User user = getUser(principal);
-		User participant = getRole(participantId).getUser();
+		Role participantRole = getRole(participantId);
 
 		Course course = courseRepository.findByIdOrThrow(courseId);
 
 		return user.isAdmin() ||
 				user.teaches(course) ||
-				user.manages(course) && !participant.teaches(course) ||
-				participant.getId().equals(user.getId());
+				user.manages(course) && !(participantRole instanceof Teacher) ||
+				participantRole.getUser().getId().equals(user.getId());
 	}
 
 	public boolean canAddParticipant(Object principal, Long courseId, String participantRole) {