code: public String joinIgnoreNull(String separator, final String keyValueSeparator) {
  		return MapUtil.joinIgnoreNull(this.map, separator, keyValueSeparator);
  	}
docs: 将map转成字符串
  
  @param separator entry之间的连接符
  @param keyValueSeparator kv之间的连接符
  @return 连接后的字符串