I've got a multi-configuration job, and created a user-defined axis "ANIMAL" with one value, "zebra". Then I ran a publisher which in perform() did:

listener.getLogger().println(build.getEnvironment(listener));

The problem is that build.getEnvironment(listener).expand("$ANIMAL") does not find anything to expand. This is because it isn't in the EnvVars. The closest thing I found is "JOB_NAME=bar/ANIMAL=zebra", but there's no "ANIMAL", which seems weird, since it is exposed as an environment variable to build-steps.