For what is worth if anyone should read again this topic(like me) the correct answer would be in DateTimeFormatter
definition, e.g.:
private static DateTimeFormatter DATE_FORMAT =
new DateTimeFormatterBuilder().appendPattern("dd/MM/yyyy[ [HH][:mm][:ss][.SSS]]")
.parseDefaulting(ChronoField.HOUR_OF_DAY, 0)
.parseDefaulting(ChronoField.MINUTE_OF_HOUR, 0)
.parseDefaulting(ChronoField.SECOND_OF_MINUTE, 0)
.toFormatter();
One should set the optional fields if they will appear. And the rest of code should be exactly the same.