diff --git a/dmp-backend/web/src/main/java/eu/eudat/logic/managers/InvitationsManager.java b/dmp-backend/web/src/main/java/eu/eudat/logic/managers/InvitationsManager.java
index 6f0c8ddb8..21d131df3 100644
--- a/dmp-backend/web/src/main/java/eu/eudat/logic/managers/InvitationsManager.java
+++ b/dmp-backend/web/src/main/java/eu/eudat/logic/managers/InvitationsManager.java
@@ -36,8 +36,10 @@ public class InvitationsManager {
         UserInfo principalUser = new UserInfo();
         principalUser.setId(principal.getId());
         invitation.getUsers().stream().filter(item -> item.getId() == null).forEach(item -> {
-			UUID id = apiContext.getOperationsContext().getDatabaseRepository().getUserInfoDao().asQueryable().where((builder, root) -> builder.equal(root.get("email"), item.getEmail())).getSingle().getId();
-			item.setId(id);
+			UserInfo existingUser = apiContext.getOperationsContext().getDatabaseRepository().getUserInfoDao().asQueryable().where((builder, root) -> builder.equal(root.get("email"), item.getEmail())).getSingleOrDefault();
+			if (existingUser != null) {
+				item.setId(existingUser.getId());
+			}
         });
         List<UserInfoInvitationModel> alreadySignedInUsers = invitation.getUsers().stream().filter(item -> item.getId() != null).collect(Collectors.toList());
         List<UserInfo> alreadySignedInUsersEntities = alreadySignedInUsers.stream().map(UserInfoInvitationModel::toDataModel).collect(Collectors.toList());