bugfix to M::History::_parse_patient_history_for_changes() - comparing original (NULL) & changed date vals caused uninitialized warning in DateTime module during auto-stringification, now vals are tested for existence (||= 'NULL') before comparison
added callback to C::WorkList::display() to display requesting username of requested test/panel; removed MooseX::AttributeHelpers from all classes - using Moose::Meta::Attribute::Native syntax
