SPDX standardizes how source code conveys its copyright and licensing
information. See https://spdx.github.io/spdx-spec/1-rationale/ . SPDX
tags are adopted in many large projects, including things like the Linux
kernel.
The pack is already has its validity checked at the beginning of the
function, so we don't need to check this again after inserting it.
Also resolves a use-after-move case.
Admiral H. Curtiss