Set query to * if '' and search export.

Cf. #22310

src/main/java/info/textgrid/services/aggregator/SearchResultList.java

@@ -63,7 +63,7 @@ public boolean hasNext() {
 	
 	protected SearchResultList(final SearchClient client, final String query, final String target, List<String> filter, boolean sandbox) {
 		this.searchClient = client;
-		this.query = query;
+		this.query = query == null || "".equals(query)? "*" : query;
 		this.filter = filter;
 		client.setTarget(target);
 		client.setSandbox(sandbox);