调用api获取sessionKey, 返回中没有unionId, 如何解决?
WxMpOAuth2AccessToken{ openId='ok4SX5LnWbW1vz_LkzzF56CLppHc', sessionKey='w0oU6Y9gLTytNvMW2RozKQ==', unionId='null'}
WxMpOAuth2AccessToken{ openId='ok4SX5LnWbW1vz_LkzzF56CLppHc', sessionKey='w0oU6Y9gLTytNvMW2RozKQ==', unionId='null'}