Reduce severity

(cherry picked from commit 03b7699973)

dmp-backend/web/src/main/java/eu/eudat/logic/managers/DataManagementPlanManager.java

@@ -138,7 +138,7 @@ public class DataManagementPlanManager {
                     items = apiContext.getOperationsContext().getDatabaseRepository().getDmpDao().asQueryable().where((builder, root) -> root.get("id").in(finalDmps.stream().map(Dmp::getId).collect(Collectors.toList())));
                 }
             } catch (Exception ex) {
-                logger.error(ex.getMessage(), ex);
+                logger.warn(ex.getMessage(), ex);
                 items = null;
             }
         }