Hello Rob, because it is not mentioned that the rider of the white horse has arrows, dosn't mean he didn't have.
If a soldier went into battle with a rifle it can be safely assumed he had bullets for the rifle.
This white horse rider went out conquering, so i would assume he had arrows to shoot from his bow.
One might say having a bow without arrows represents him conquering through peace. If that is so then why the bow?
if one is travelling up a river in a row boat, there is no need to mention he has oars.