Set creation and modification date in Etude::prePersist only if not set before.
Set creation and modification date in Etude::prePersist only if not set before.

n7consulting/Incipio,M-GaTE/Jeyser,N7-Consulting/Incipio,N7-Consulting/Incipio,n7consulting/Incipio,N7-Consulting/Incipio,M-GaTE/Jeyser,M-GaTE/Jeyser,n7consulting/Incipio,N7-Consulting/Incipio,M-GaTE/Jeyser