Change empty to !isset call to check if there are any keys present on _groupKeys method
Change empty to !isset call to check if there are any keys present on _groupKeys method

Add condition to avoid indexed array with empty string when key is null but the result keys set is already set.

CakeDC/cakephp,ADmad/cakephp,CakeDC/cakephp,ndm2/cakephp,ndm2/cakephp,cakephp/cakephp,cakephp/cakephp,cakephp/cakephp,CakeDC/cakephp,ADmad/cakephp,CakeDC/cakephp,ADmad/cakephp,ndm2/cakephp,ndm2/cakephp,ADmad/cakephp,cakephp/cakephp