Sadly, no. First, it would not be void ab initio. Past that, your issue is that the express terms of the contract appear to allow that, so you will lose regard

Sadly, no. First, it would not be void ab initio. Past that, your issue is that the express terms of the contract appear to allow that, so you will lose regardless of whether that was a good idea for you to do :P You could argue breach of good faith, etc, but not unjust enrichment. Like restitution, unjust enrichment is a theory of implied contracts. You can plead it and breach of express contract at the same time, but you can only recover for one, and you will not recover for unjust enrichment if the court finds an express contract.