Fixes#2067
**Description**
This PR fixes an issue where Go's `append` returns `nil` when appending
an empty slice to a nil slice.
I added a check in `SafeCopy` to ensure we always return `[]byte{}` in
this case, along with a new unit test.
I also verified it using the test offered in the issue
**Checklist**
- [x] Code compiles correctly and linting passes locally
- [ ] For all _code_ changes, an entry added to the `CHANGELOG.md` file
describing and linking to
this PR
- [x] Tests added for new functionality, or regression tests for bug
fixes added as applicable
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Co-authored-by: Matthew McNeely <matthew.mcneely@gmail.com>
