Take a reference to a non-POD event.
If a plugin receives an event with type 0, it means the event is a pointer to some object in memory and not a flat sequence of bytes in the buffer. When receiving a non-POD event, the plugin already has an implicit reference to the event. If the event is stored AND passed to an output, lv2_event_ref MUST be called on that event. If the event is only stored OR passed through, this is not necessary (as the plugin already has 1 implicit reference).