handle undefined ref

[james-bruten-mo]

PR Summary

Sci/Tech Reviewer:
Code Reviewer: @t00sa

If ref isn't defined treat it as an empty string, rather than a None

Code Quality Checklist

• I have performed a self-review of my own code
• My code follows the project's style guidelines
• Comments have been included that aid understanding and enhance the readability of the code
• My changes generate no new warnings
• All automated checks in the CI pipeline have completed successfully

Testing

• This change has been tested appropriately (please describe)

Security Considerations

• I have reviewed my changes for potential security issues
• Sensitive data is properly handled (if applicable)
• Authentication and authorisation are properly implemented (if applicable)

AI Assistance and Attribution

• Some of the content of this change has been produced with the assistance of Generative AI tool name (e.g., Met Office Github Copilot Enterprise, Github Copilot Personal, ChatGPT GPT-4, etc) and I have followed the Simulation Systems AI policy (including attribution labels)

Sci/Tech Review

• I understand this area of code and the changes being added
• The proposed changes correspond to the pull request description
• Documentation is sufficient (do documentation papers need updating)
• Sufficient testing has been completed

(Please alert the code reviewer via a tag when you have approved the SR)

Code Review

• All dependencies have been resolved
• Related Issues have been properly linked and addressed
• Code quality standards have been met
• Tests are adequate and have passed
• Security considerations have been addressed
• Performance impact is acceptable

[t00sa]

I swapped things round to make shumlib the dependency with an empty ref and ran with your branch of scripts, and the task falls over at a different point:

Traceback (most recent call last):
  File "/data/scratch/sam.clarke/cylc-run/UM-Socrates14/run9/work/1/extract_source/rose_stem_extract_source.py", line 76, in <module>
    main()
  File "/data/scratch/sam.clarke/cylc-run/UM-Socrates14/run9/work/1/extract_source/rose_stem_extract_source.py", line 55, in main
    get_source(
  File "/data/scratch/sam.clarke/cylc-run/UM-Socrates14/run9/work/1/extract_source/get_git_sources.py", line 113, in get_source
    clone_repo(source, ref, dest)
  File "/data/scratch/sam.clarke/cylc-run/UM-Socrates14/run9/work/1/extract_source/get_git_sources.py", line 286, in clone_repo
    run_command(command)
  File "/data/scratch/sam.clarke/cylc-run/UM-Socrates14/run9/work/1/extract_source/get_git_sources.py", line 49, in run_command
    raise subprocess.CalledProcessError(
subprocess.CalledProcessError: Command '['git', '-C', '/home/users/sam.clarke/cylc-run/UM-Socrates14/run9/share/source/shumlib', 'fetch', 'origin', 'None']' returned non-zero exit status 128.

[t00sa]

PICNIC error on my part: rose-stem/app/extract_source/rose-app.conf was still pointing at the main version. Now passing.

[t00sa]

Looks good to me