A "portfolio" does not have to, and should not, consist of side projects. Don't have any real code that you are allowed to share? Obviously, many employers won't hire engineers without reviewing existing code or having you engage in a coding exercise, but here's an idea: take a bunch of screenshots of public-facing applications/functionality you've built for your current and/or past employers. With WordPress and a $25 portfolio theme, you can have a decent-looking showcase of your work product up and running in a matter of hours.
If you have absolutely nothing that you can share (code, screenshots, a URL, a "case study") with a prospective employer, it's not the prospective employer that has a problem.