AIP-231 Requires Parent even though parent is not needed for top level resources.

Thanks for stopping by to let us know something could be better!

**PLEASE READ**: If you have a support contract with Google, please create an issue in the [support console](https://cloud.google.com/support/) instead of filing on GitHub. This will ensure a timely response.

Is this a client library issue or a product issue? We will only be able to assist with issues that pertain to the behaviors of this library. If the issue you're experiencing is due to the behavior of the product itself, please visit the [Support page](https://cloud.google.com/support) to reach the most relevant engineers.

If the support paths suggested above still do not result in a resolution, please provide the following details.

#### Environment details

- Programming language: proto
- OS: n/A
- Language runtime version: N/A
- Package version: N/A

#### Steps to reproduce

1. Create a BatchGet of a top level resource.
2. Linter complains, requiring parent field.

Making sure to follow these steps will guarantee the quickest resolution possible.

Thanks!