code: static void init() {
          contextMap = null;
          final PropertiesUtil managerProps = PropertiesUtil.getProperties();
          disableAll = managerProps.getBooleanProperty(DISABLE_ALL);
          useStack = !(managerProps.getBooleanProperty(DISABLE_STACK) || disableAll);
          useMap = !(managerProps.getBooleanProperty(DISABLE_MAP) || disableAll);
  
          contextStack = new Log4jv2ThreadContextStack(useStack);
          contextMap = new Log4jv2ThreadContextMap();
      }
docs: <em>Consider private, used for testing.</em>