How to search a word that is a empty brackets

[xuziheng1002]

We have some logs with barckets, like “2019-09-27 12:00:00 jobs running at ”.

So we want to search the word that is a empty brackets ,
like this:

and I tried many way to search it including regular expression, but all failed,

please let me know if anybody has solution~~

[jan (Jan Doberstein)]

did you “escape” your search?

http://docs.graylog.org/en/3.1/pages/queries.html#escaping

[xuziheng1002]

I search with // and “” , both way is NG

[xuziheng1002]