code: public void clear() {
  
          /**
           * Unfortunately log4j's MDC historically never had a mechanism to block remove keys,
           * so we're forced to do this one by one.
           */
          for (String key : allKeys()) {
             mdcBridge.remove(key);
          }
  
          PER_THREAD_CONTEXTS.getUnchecked(Thread.currentThread()).clear();
      }
docs: Clears all values for the current thread.