Currently our code base is inconsistent regarding the way a set of DataNodes are returned. We have at least 3 prominent styles.

itk::VectorContainer<unsigned int, DataNode::Pointer> (e.g. DataStorage::SetOfObjectes)
std::vector<DataNode::ConstPointer>
QList<DataNode::Pointer>

Variant 1 is used in the context of the data storage.
Variant 2 was used e.g. heavily when the statistics where reworked in 2018/2019 and in code parts without Qt.
Variant 3 is used everywhere near Blueberry and plugins and BlueBerry selections. (This is the reason e.g. while all the new selection widgets use this type).

1. We will move the helper functions that convert between const and non-const node pointers for V1<->V2 to mitkCore to use vor everyone. The conversion with same constness is easy anyways.
2. We will move the helper functions that convert between V2<->V3 to QtWidgets module to be accessible for all that use Qt.

The helper functions where so far introduced by ralf in the StatisticsUI module.