fixed topic query where sortby would be null, which leads to a npe

vipra-util/src/main/java/de/vipra/util/service/DatabaseService.java

@@ -3,6 +3,7 @@ package de.vipra.util.service;
 import java.util.List;
 
 import org.mongodb.morphia.Datastore;
+import org.mongodb.morphia.query.Query;
 
 import de.vipra.util.Config;
 import de.vipra.util.Constants;
@@ -28,7 +29,11 @@ public class DatabaseService<T extends Model> implements Service<T, DatabaseExce
 	}
 
 	public List<T> getMultiple(int skip, int limit, String sortBy) {
-		return datastore.createQuery(clazz).offset(skip).limit(limit).order(sortBy).asList();
+		Query<T> q = datastore.createQuery(clazz).offset(skip).limit(limit);
+		if (sortBy != null)
+			q = q.order(sortBy);
+		List<T> list = q.asList();
+		return list;
 	}
 
 	@Override