Fix critical issue with xml import

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

@@ -1679,7 +1679,7 @@ public class DataManagementPlanManager {
             if (dataManagementPlans.get(0).getPublicDate() != null) {
                 extraPropertiesMap.put("publicDate", dataManagementPlans.get(0).getPublicDate());
             }
-            if (dataManagementPlans.get(0).getCosts() != null) {
+            if (dataManagementPlans.get(0).getCosts() != null && !dataManagementPlans.get(0).getCosts().isEmpty()) {
                 extraPropertiesMap.put("costs", mapper.readValue(dataManagementPlans.get(0).getCosts(), ArrayList.class));
             }
             dm.setExtraProperties(extraPropertiesMap);