Missing ETag response header for CSS TransformedResources

Version: Spring Boot 2.3.4.RELEASE

When using a content resource chain to cache-bust .css and .js files, with server compression enabled, and Thymeleaf as the template engine (not sure if it's relevant or not), the css file is compressed but the js file is not.
If the JS file is requested directly (without going through the resource chain), then it's compressed.

Here's a complete minimal repro: https://github.com/jnizet/compressiondemo

Here's a screenshot of the Chrome network panel when loading the page:

As you can see, the bundle.js files (which did not go through the resource chain) has a transfer size that is less than the file size. But the bundle.c525abb....js file, which is the same file, but obtained through the resource chain, is not compressed.

What's weird is that the css file did go through the resource chain, but was compressed as expected.

Start with the linked compressiondemo minimal reproduction and inspect requests for CSS and JavaScript resources served through the content resource chain versus direct requests. Compare compression and response headers, including the missing ETag reported for CSS TransformedResources; done means the transformed JavaScript behaves consistently with the direct resource and the expected ETag header is present.