make release issue 10.3

I want to create a customized FreeBSD release 10.3. When I run make release, it created the iso file with 550M, and in the ftp folder, the src.txz is empty. I believe 550M doesn't include the source since I also created customized version 10.2, and iso is 700M. What can I do to include the source in the release build? Any pointers would be great, thanks!
I don't know how can I include the src.txz to build.
It will be included unless you specifically turn it off.

     NOSRC        If set, do not include system source code in the release.