There's a default in https://github.com/edx/edx-platform/blob/6f9a005957a4de660927cae29e4be3d62a016645/lms/envs/common.py#L35, if that's what you mean. I figured the `PLATFORM_NAME` was a must-have in the `env.json` file, much like `SITE_NAME` on https://github.com/edx/edx-platform/blob/6f9a005957a4de660927cae29e4be3d62a016645/lms/envs/aws.py#L104