issues with icon error

[Chonghe-Jiang]

I am just trying to get the Academic theme for Hugo up and running.The hugo version is 0.81.When I type in the
hugo server --watch --theme=Academic
There exists error as follow
"D:\homepage\geb.im\themes\Academic\content\authors\admin\_index.md:77:1": failed to extract shortcode: template for shortcode "icon" not found
I tried to solve the problem according to https://discourse.gohugo.io/t/failed-to-extract-shortcode/16504/2 but it doesn't work out.
What can I do?Thanks a lot!