# What does this PR do?
Fixes a crash that occurred when building a stack as a container image
via the interactive wizard without supplying --template or --config.
- Root cause: template_or_config was None; only the container path
relies on that parameter, which later reaches subprocess.run() and
triggers
`TypeError: expected str, bytes or os.PathLike object, not NoneType.`
- Change: in `_run_stack_build_command_from_build_config` we now fall
back to the freshly‑written build‑spec file whenever both optional
sources are missing. Also adds a spy‑based unit test that asserts a
valid string path is passed to build_image() for container builds.
### Closes#1976
## Test Plan
- New unit test: test_build_path.py. Monkey‑patches build_image,
captures the fourth argument, and verifies it is a real path
- Manual smoke test:
```
llama stack build --image-type container
# answer wizard prompts
```
Build proceeds into Docker without raising the previous TypeError.
## Future Work
Harmonise `build_image` arguments so every image type receives the same
inputs, eliminating this asymmetric special‑case.
