since the ast AnnAssign class can be value-less, avoid resolution fai…

[speediedan]

Thanks so much to everyone in the community (especially @mauvilsa !) for this immensely valuable package!

This PR fixes #147.

What does this PR do?

According to the current cpython abstract grammar definition, the value of an ast.AnnAssign class can be None (also discussed in PEP 526) whether within methods or in the class body. So though it's usually considered bad practice stylistically, since it's valid syntax, AST-based parameter resolution should handle this edge case I think.

I've written a tiny one-line fix for this issue and added an associated test in the parameter-resolver test module.

In case it's relevant, an alternate approach to testing that I validated was to simply add a value-less annotation within the __init__ method of ClassA but I ultimately decided that isolating the test the way I've done in this PR might make more sense.

• Did you read the contributing guideline?
• [n/a] Did you update the documentation? (readme and public docstrings)
• Did you write unit tests such that there is 100% coverage on related code? (required for bug fixes and new features)
• Did you verify that new and existing tests pass locally?
• Did you make sure that all changes preserve backward compatibility?
• Did you update the CHANGELOG? (not for typos, docs, test updates, or minor internal changes/refactors)

[codecov-commenter]

Codecov Report

Merging #148 (f241f0e) into master (c989d91) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #148   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           18        18           
  Lines         4170      4171    +1     
=========================================
+ Hits          4170      4171    +1     

Flag	Coverage Δ
py3.10_all	99.90% <100.00%> (+<0.01%)	⬆️
py3.6	91.02% <100.00%> (+<0.01%)	⬆️
py3.6_all	99.68% <100.00%> (+<0.01%)	⬆️
py3.7_all	99.80% <100.00%> (+<0.01%)	⬆️
py3.8	91.29% <100.00%> (+<0.01%)	⬆️
py3.8_all	99.88% <100.00%> (+<0.01%)	⬆️
py3.9_all	99.88% <100.00%> (+<0.01%)	⬆️

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Impacted Files	Coverage Δ
jsonargparse/parameter_resolvers.py	100.00% <100.00%> (ø)

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[mauvilsa]

Looks great, thank you! This fixes a bug, so please do add an entry in the Fixed section of the changelog.

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication

[speediedan]

Looks great, thank you! This fixes a bug, so please do add an entry in the Fixed section of the changelog.

Done! Thanks again for your invaluable contribution to the community with this package. I look forward to continuing using it in the future!