docs: public String put(String group, String key, String value) {
  		group = StrUtil.nullToEmpty(group).trim();
  		writeLock.lock();
  		try {
  			LinkedHashMap<String, String> valueMap = this.get(group);
  			if (null == valueMap) {
  				valueMap = new LinkedHashMap<>();
  				this.put(group, valueMap);
  			}
  			this.size = -1;
  			return valueMap.put(key, value);
  		} finally {
  			writeLock.unlock();
  		}
  	}