Check if string_names is None before returning string_names

[Leo-Ryu]

Hello!

I'm using jedi for a personal project, and I was getting this error when generating references of a class.

This PR simply checks if self.string_names is None and returns an empty list if so-- it solves the issue on my personal project so I thought it might be of some use to others.

  File "/Users/lryu/.local/share/virtualenvs/python-parser-S0EswWrV/lib/python3.8/site-packages/jedi/api/helpers.py", line 487, in wrapper
    return func(self, line, column, *args, **kwargs)
  File "/Users/lryu/.local/share/virtualenvs/python-parser-S0EswWrV/lib/python3.8/site-packages/jedi/api/__init__.py", line 529, in get_references
    return _references(**kwargs)
  File "/Users/lryu/.local/share/virtualenvs/python-parser-S0EswWrV/lib/python3.8/site-packages/jedi/api/__init__.py", line 523, in _references
    names = find_references(self._get_module_context(), tree_name, scope == 'file')
  File "/Users/lryu/.local/share/virtualenvs/python-parser-S0EswWrV/lib/python3.8/site-packages/jedi/inference/references.py", line 150, in find_references
    new = _dictionarize(_find_names(module_context, name_leaf))
  File "/Users/lryu/.local/share/virtualenvs/python-parser-S0EswWrV/lib/python3.8/site-packages/jedi/inference/references.py", line 75, in _find_names
    found_names = set(name.goto())
  File "/Users/lryu/.local/share/virtualenvs/python-parser-S0EswWrV/lib/python3.8/site-packages/jedi/inference/names.py", line 155, in goto
    module_names = goto_import(context, name)
  File "/Users/lryu/.local/share/virtualenvs/python-parser-S0EswWrV/lib/python3.8/site-packages/jedi/inference/cache.py", line 44, in wrapper
    rv = function(obj, *args, **kwargs)
  File "/Users/lryu/.local/share/virtualenvs/python-parser-S0EswWrV/lib/python3.8/site-packages/jedi/inference/imports.py", line 77, in goto_import
    _prepare_infer_import(module_context, tree_name)
  File "/Users/lryu/.local/share/virtualenvs/python-parser-S0EswWrV/lib/python3.8/site-packages/jedi/inference/imports.py", line 115, in _prepare_infer_import
    importer = Importer(module_context.inference_state, tuple(import_path),
  File "/Users/lryu/.local/share/virtualenvs/python-parser-S0EswWrV/lib/python3.8/site-packages/jedi/inference/imports.py", line 177, in __init__
    base = module_context.get_value().py__package__()
  File "/Users/lryu/.local/share/virtualenvs/python-parser-S0EswWrV/lib/python3.8/site-packages/jedi/inference/value/module.py", line 186, in py__package__
    return self.string_names[:-1]

[davidhalter]

Thanks for the fix! Is there a way we can regression test this, so it won't happen again in the future?

[codecov-io]

Codecov Report

Merging #1708 (4e5bd33) into master (42a759a) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1708   +/-   ##
=======================================
  Coverage   94.52%   94.52%           
=======================================
  Files          79       79           
  Lines       11762    11764    +2     
=======================================
+ Hits        11118    11120    +2     
  Misses        644      644           

Impacted Files	Coverage Δ
jedi/inference/value/module.py	99.21% <100.00%> (+0.01%)	⬆️

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[Leo-Ryu]

@davidhalter Happy to help! I implemented a simple test-- let me know if you'd like something more complex

[davidhalter]

flake8 fails: https://travis-ci.org/github/davidhalter/jedi/jobs/748914635

Test is fine I guess, will have to check if it actually changed the coverage.