https://forum.qt.io/topic/86749/qdateedit-qabstractspinbox-blank-empty-value-problem/5
QDateEdit (QAbstractSpinBox) blank/empty value problem | Qt Forum
Jan 12, 2018 - @mrjj Unfortunately, you seem to be confirming my understanding of the lack of support for empty dates/numbers/etc. in all the QAbstractSpinBox-derived class...
empty valueblankproblemqtforum