docs: public Map<String, SubsystemInformation> getAvailableSubsystems(String moduleName) {
          Map<String, SubsystemInformation> result = null;
          final ExtensionInfo info = extensions.get(moduleName);
          if (info != null) {
              //noinspection SynchronizationOnLocalVariableOrMethodParameter
              synchronized (info) {
                  result = Collections.unmodifiableMap(new HashMap<String, SubsystemInformation>(info.subsystems));
              }
          }
          return result;
      }