If a ship has no dice results to change into Evade results, then an evade token is useless to it. The Ghost could still use an evade token if it's getting a range 3 defense bonus, and/or the attack is obstucted by an obstacle. But often that won't be the case for the Ghost.
It's one of the major changes to defense in second edition. Dice modification is rarer and generally weaker. On the plus side, you can spend multiple evade tokens on a single evade roll now, in case you happen to gain multiple evades (for example, TIE/D Defender can do so every turn).