QActionGroup allowing unchecking ?

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Hello,

I have a few checkable QAction, grouped using a QActionGroup to avoid having 2 QAction checked at the same time.
My problem is that the side effect of QActionGroup is that it doesn't allow the user to uncheck any QAction:
once one of the QAction from the group is checked, the group stay checked, no way to uncheck every QAction from this group.
What can I do to prevent this behaviour ?

Thanks !