Missing ROOT key causes NPE in JarClassesAnalysis for malformed MR-JARs

[elharo]

In JarClassesAnalysis.java:153-155:

JarVersionedRuntime rootContentVersionedRuntime = runtimeVersionsMap.remove(ROOT);
jarData.setRootEntries(rootContentVersionedRuntime.getEntries());  // NPE if no ROOT

If a malformed multi-release JAR has no root-level entries (every entry is under META-INF/versions/N/), runtimeVersionsMap has no ROOT key, remove(ROOT) returns null, and .getEntries() throws a NullPointerException.

Fix: Guard against null:

JarVersionedRuntime rootContent = runtimeVersionsMap.remove(ROOT);
if (rootContent != null) {
    jarData.setRootEntries(rootContent.getEntries());
}