@Listener
public void onBlockBreak(ChangeBlockEvent.Break evt, @Root Player player) {
    //go through all changes (will mostly be only one)
    for (Transaction<BlockSnapshot> tr : evt.getTransactions()) {
        //check if the original state was a LOG
        if (tr.getOriginal().getState().getType() != BlockTypes.LOG) {
            //if not, set the transaction invalid
            tr.setValid(false);
        }
    }
}