I want to build 1.2.2019Q4 labelled repo from github vyos-build, but when I build it, it does not contain json support. What affects the json support for output iso, is it linux kernel or another depending package?

I want to build 1.2.2019Q4 labelled repo from github vyos-build, but when I build it, it does not contain json support. What affects the json support for output iso, is it linux kernel or another depending package ?