cubicweb #2473469 entity.dc_date() returns an error [open]

Any use of the dc_date() method of an entity returns the following error:

AttributeError: 'unicode' object has no attribute 'strftime'

(detected in cubicweb 3.15.3 under Ubuntu 12.04, with sqlite as database engine)

priorityimportant
typebug
done in<not specified>
closed by<not specified>