getJarClasses() throws NPE for missing version key in JarVersionedRuntimes

[elharo]

In JarVersionedRuntimes.java:47-49:

public JarClasses getJarClasses(Integer version) {
    return versionedRuntimeMap.get(version).getJarClasses();  // NPE if version absent
}

If the requested version is not a key in the map, get(version) returns null, then .getJarClasses() throws a NullPointerException. This is inconsistent with getJarVersionedRuntime() on the same class, which safely returns null for missing keys. Any caller querying a non-existent version will crash.

Fix: Guard against null, e.g.:

JarVersionedRuntime runtime = versionedRuntimeMap.get(version);
return runtime != null ? runtime.getJarClasses() : null;