I have just found out that ClassPoolRepository is registering null class loaders.

JBossClDelegatingClassPoolFactory.create method has a call to registerBootstrapClassLoaders

public synchronized AbstractClassPool create(ClassLoader cl, ClassPool src, ScopedClassPoolRepository repository)
   {
      if (this.currentClassLoaders.contains(cl))
      {
         return null;
      }
      currentClassLoaders.add(cl);
      try
      {
         ClassPool parent = getCreateParentClassPools(cl, src, repository);
         
         if (cl instanceof RealClassLoader)
         {
            Module module = registry.getModule(cl);
            if (module == null)
            {
               module = getModuleForClassLoader(cl);
            }
            registerModuleCallback.registerModule(module);
 --->           registerBootstrapLoaders(module, repository);
...
}

This is the implementation of registerBootstrapLoaders:

private void registerBootstrapLoaders(Module skip, ScopedClassPoolRepository repository)
   {
      Collection<Module> unregistered = registerModuleCallback.getUnregisteredModules();
      if (unregistered.size() > 0)
      {
         for (Module module : unregistered)
         {
            if (module == skip)
            {
               continue;
            }
            ClassLoader loader = getClassLoaderForModule(module);
            if (this.currentClassLoaders.contains(loader))
            {
               continue;
            }
            ClassPool classPool = repository.registerClassLoader(loader);
            if (classPool == null)
            {
               repository.unregisterClassLoader(loader);
            }
         }
      }
   }

The problem is that many of those modules, if not all, have a null class loader at this point.

I'll try skipping the registration of such modules to see if any test breaks. Does anybody has a better idea on how to fix this?