This PR was merged into the 3.3-dev branch.Discussion----------[DI] Allow ~ instead of {} for services in Yaml| Q             | A| ------------- | ---| Branch?       | master| Bug fix?      | no| New feature?  | no| BC breaks?    | no| Deprecations? | no| Tests pass?   | yes| Fixed tickets | -| License       | MIT| Doc PR        | -Now we can omit the class name, Yaml config can look like this:```yamlservices:    AppBundle\Something: {}```While this works, the consistent way in Symfony for such cases is to use `~`. This PR allows to use `~` as well, ending up with:```yamlservices:    AppBundle\Something: ~```Commits-------28a1b5a Allow setting services as null