diff --git a/src/main/java/de/ids_mannheim/korap/query/serialize/CQLTree.java b/src/main/java/de/ids_mannheim/korap/query/serialize/CQLTree.java
index 92f74e5..bef19a1 100644
--- a/src/main/java/de/ids_mannheim/korap/query/serialize/CQLTree.java
+++ b/src/main/java/de/ids_mannheim/korap/query/serialize/CQLTree.java
@@ -55,7 +55,10 @@
     }
 
     @Override
-    public void process(String query) throws QueryException {
+    public void process(String query) throws QueryException {    	
+    	 if ((query == null) || query.isEmpty()) 
+             throw new QueryException(27, "An empty query is unsupported.");
+    	
         CQLNode cqlNode = parseQuerytoCQLNode(query);
         parseCQLNode(cqlNode);
         ObjectMapper mapper = new ObjectMapper();