`null` will be a reserved keyword in PHP 7. This patch renames the `Null` mail transport to `InMemory`, and updates the factory to return an `InMemory` instance whenever `null` is retrieved. A future patch will re-add the `Null` transport with an `E_USER_DEPRECATION` notice.
`object` will be a reserved word in PHP 7, and, as such, we cannot use it as an annotation class name. `Instance` was chosen, and `Object` has been altered to extend `Instance` and emit an `E_USER_DEPRECATED` notice on instantiation.