We pass `null` for the class name here:

https://github.com/elastic/elasticsearch/blob/f086dd18ddc705bf84a1ff99d35196ec2498fd52/server/src/main/java/org/elasticsearch/plugins/PluginDescriptor.java#L261

However the class name is mandatory for the transport protocol today:

https://github.com/elastic/elasticsearch/blob/f086dd18ddc705bf84a1ff99d35196ec2498fd52/server/src/main/java/org/elasticsearch/plugins/PluginDescriptor.java#L156

This prevents various APIs from working in a cluster with stable plugins installed.
server/src/main/java/org/elasticsearch/TransportVersions.java
* SS - The serverless version part. It should always be 00 here, it is used by serverless only.
     * P - The patch version part
     *
     * To determine the id of the next TransportVersion constant, do the following:
     * - Use the same major version, unless bumping majors
     * - Bump the server version part by 1, unless creating a patch version
     * - Leave the serverless part as 00
     * - Bump the patch part if creating a patch version
     *
     * If a patch version is created, it should be placed sorted among the other existing constants.
     *
     * REVERTING A TRANSPORT VERSION
     *
     * If you revert a commit with a transport version change, you MUST ensure there is a NEW transport version representing the reverted
     * change. DO NOT let the transport version go backwards, it must ALWAYS be incremented.
     *
     * DETERMINING TRANSPORT VERSIONS FROM GIT HISTORY
     *
     * If your git checkout has the expected minor-version-numbered branches and the expected release-version tags then you can find the
     * transport versions known by a particular release ...
     *
     *     git show v8.9.1:server/src/main/java/org/elasticsearch/TransportVersions.java | grep def
     *
     * ... or by a particular branch ...
     *
     *     git show 8.10:server/src/main/java/org/elasticsearch/TransportVersions.java | grep def
     *
     * ... and you can see which versions were added in between two versions too ...
     *
     *     git diff 8.10..main -- server/src/main/java/org/elasticsearch/TransportVersions.java