PocoAbstractDao: define template method whenNull
PocoAbstractDao: define template method whenNull

Generalize situations when we want to return a default
value of data that are empty (or NULL).

Signed-off-by: Jan Viktorin <3eab6ac54c005c4408f608556a6663b7f2abede7@fit.vutbr.cz>

BeeeOn/server,BeeeOn/server,BeeeOn/server,BeeeOn/server