var as = _p.as('client');
var cell = as.cell();
var role = cell.ctl.role.retrieve({ 'Name': 'testapp-read', '_Box.Name': 'test-app' });
var extCell = cell.ctl.extCell.retrieve('http://localhost/testcell-002/');
role.extCell.link(extCell); <--- Failed
e.g.