docs: public GroupedMap clear(String group) {
  		group = StrUtil.nullToEmpty(group).trim();
  		writeLock.lock();
  		try {
  			final LinkedHashMap<String, String> valueMap = this.get(group);
  			if (MapUtil.isNotEmpty(valueMap)) {
  				valueMap.clear();
  			}
  		} finally {
  			writeLock.unlock();
  		}
  		return this;
  	}