Accessing property name of undefined

[micahriggan]

This line below will cause an unhandled, since event isn't defined

539     if (!event) {
540         throw new Error('Event "' + event.name + '" doesn\'t exist in this contract.');
541     }

https://github.com/ethereum/web3.js/blob/2022b17d52d31ce95559d18d5530d18c83eb4d1c/packages/web3-eth-contract/src/index.js#L540