[Zope] empty lines property value

I just noticed that a property of type "lines", when created via the management interface (if not by other means as well) has as its initial value ['']. I would have expected an empty "lines" property to have the value []. Does anyone know the rationale behind this? Or should it be considered a bug? I see this behavior in both of the versions of Zope that we run locally -- 2.2.4 and 2.3.1b1.