Remove null values from configuration file.

[gouttegd]

Automatically generated configuration files (obtained by seeding a repository without a provided configuration file) contain explicit null values for all settings that do not have a default value and do not have been explicitly set on the command line.

Such values (i) may cause problems downstream of parsing the configuration, and (ii) needlessly pollute the configuration file.

We take care of both problems by

• adding a purge_null_values method to explicitly clean a dictionary of any null values;
• using that new method in two occasions:
  • when saving the configuration (so that an automatically generated or updated file never contains null values in the first place);
  • after parsing the configuration and before trying to update it (in case a file would still somehow contain null values).

closes #31

[matentzn]

Nice, two optional thoughts

[matentzn]

One thing you should contemplate before merging, but I leave this up to your judgment:

null means "use the default" everywhere, and for a few options the default isn't empty. Concretely, a config with

ci:
workflows:

gives you ci = ['github_actions'] and workflows = ['docs', 'qc']

Since this works:

ci: []
workflows: []

I am fine to say: lets deal with this with docs; Your judgment.

[matentzn]

Sorry meant to approve with last comment

[gouttegd]

null means "use the default" everywhere, and for a few options the default isn't empty. > Concretely, a config with

ci:
workflows:

gives you ci = ['github_actions'] and workflows = ['docs', 'qc']

Actually such a config gives an error (just tested with ODK 1.6.1):

Traceback (most recent call last):
  File "/tools/odk.py", line 1511, in <module>
    cli()
  File "/usr/local/lib/python3.12/dist-packages/click/core.py", line 1161, in __call__
    return self.main(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/dist-packages/click/core.py", line 1082, in main
    rv = self.invoke(ctx)
         ^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/dist-packages/click/core.py", line 1697, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/dist-packages/click/core.py", line 1443, in invoke
    return ctx.invoke(self.callback, **ctx.params)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/dist-packages/click/core.py", line 788, in invoke
    return __callback(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/tools/odk.py", line 1441, in seed
    tgts += install_template_files(mg, templatedir, outdir, policies)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/tools/odk.py", line 1061, in install_template_files
    s.write(generator.generate(srcf))
            ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/tools/odk.py", line 890, in generate
    return template.render( project = self.context.project, env = {"ODK_VERSION": os.getenv("ODK_VERSION")})
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/dist-packages/jinja2/environment.py", line 1295, in render
    self.environment.handle_exception()
  File "/usr/local/lib/python3.12/dist-packages/jinja2/environment.py", line 942, in handle_exception
    raise rewrite_traceback_stack(source=source)
  File "<template>", line 1, in top-level template code
TypeError: argument of type 'NoneType' is not iterable

So since using empty values (either implicitly, as in ci:, or explicitly, as in ci: null) is not in fact currently supported, we are not loosing anything.

Without this PR:

• if you want the default, just omit the key entirely;
• if you want an empty list of workflows, explicitly set an empty list (workflows: [])
• if you set the key to nothing (workflows: or workflows: null), you get the error above.

With this PR:

• if you want the default, either omit the key entirely or set it to nothing;
• if you want an empty list of workflows, explicitly set an empty list.