still have bugs when querying children().list().setQ() H

still have bugs when querying children().list().setQ() H

String queryString2 = " title ='" + currentSubFolder+ "'";
@@@@@Children.List request_2 =
service.children().list(mainFolder_Id).setQ(queryString2);
@@@@@ChildList files = request_2.execute();
@@@
it will return
08-15 00:18:10.656: W/System.err(12563):
com.google.api.client.googleapis.json.GoogleJsonResponseException: 500
Internal Server Error
08-15 00:18:10.656: W/System.err(12563):
com.google.api.client.googleapis.json.GoogleJsonResponseException: 500
Internal Server Error
08-15 00:18:10.656: W/System.err(12563): {
08-15 00:18:10.656: W/System.err(12563): "code": 500,
08-15 00:18:10.656: W/System.err(12563): "errors": [
08-15 00:18:10.656: W/System.err(12563): {
08-15 00:18:10.656: W/System.err(12563): "domain": "global",
08-15 00:18:10.656: W/System.err(12563): "message": "Internal Error",
08-15 00:18:10.656: W/System.err(12563): "reason": "internalError"
08-15 00:18:10.656: W/System.err(12563): }
08-15 00:18:10.656: W/System.err(12563): ],
08-15 00:18:10.656: W/System.err(12563): "message": "Internal Error"
08-15 00:18:10.656: W/System.err(12563): }
still have bugs in java client api not be fixxed? But I tested JAVASCRIPT
api online seems can query with Query field yesterday.