Posted v2 patch, issue was that I changed it to be more consistent with documentation e.g. for
SPDX_IMAGE_SUPPLIER:
If not set, no supplier information is added to the image SBOM
but maybe it meant that if `<PREFIX>_*` is not set (e.g. _name or _type), then this information is not added.
So with this change it'll be possible to use `SPDX_IMAGE_SUPPLIER = "MY_COMPANY"` or undocumented `SPDX_IMAGE_SUPPLIER_ref = "MY_COMPANY"` (which doesn't pass all arguments it was called with (e.g. `add`), so it feels like a bug but I don't know enough about this subsystem to tell) with variable with no suffix having priority.
Another way to fix it would be to maybe change documentation and say explicitly to use SPDX_IMAGE_SUPPLIER_ref and that SPDX_IMAGE_SUPPLIER without any suffix is not used.