Cannot get planned_in from requirement

[yuxisun1217]

When I get planned_in in a requirement, it can show a Plan object in the list, but all the attributions are empty.

Python 2.7.5 (default, Jun 11 2019, 14:33:56) 
[GCC 4.8.5 20150623 (Red Hat 4.8.5-39)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> from pylero.work_item import Requirement
>>> wi = Requirement('PLANXXX', 'ITEM-41685')
>>> pl = wi.planned_in
>>> pl
[<pylero.plan.Plan object at 0x7f048ca7f990>]
>>> pl.name
>>> pl.plan_id
>>> pl.description