I cannot add a layergroup in another layergroup

geosercer version 2.12x ,geoserver manager version 1.7.0
i published the two layergroups(yapailayer,myGroup) in the same workspace(sf),they hava the same ESPG:900913.
and then i used the codes to add layergroup yapailayer to the layergroup myGroup:
GSLayerGroupEncoder23 layergroupencoder = new GSLayerGroupEncoder23();
layergroupencoder.addLayerGroup("yapailayer");
boolean bl = publisher.configureLayerGroup("sf", "myGroup",layergroupencoder );

the resule always is :Caused by: java.lang.IllegalArgumentException: Layer group must not be empty.

ps:i can add layer in the layergroup.
my english is bad,hope you can understand me and help me.

ok,I've solved it.