default Merger<ENTITY> merger() {
        return entity -> {
            try {
                persister().apply(entity);
                return entity;
            } catch (SpeedmentException se) {
                updater().apply(entity);
                return entity;
            }
        };
    }
Returns a {@link Merger} which can be used to merge
entities in the underlying database.
@see Merger#apply

@return a Merger
runtime-parent/runtime-core/src/main/java/com/speedment/runtime/core/manager/PersistenceProvider.java