Fix type hint mismatches with None defaults throughout codebase

[Copilot]

What does this changes

Comprehensively fixes type hint inconsistencies where parameter defaults are None but type hints don't include None. Changes are made in two phases:

Phase 1: Empty String Conversion (4 parameters)

• Replaces str = None with str = "" where empty string is semantically equivalent
• Updates conditional checks and docstrings accordingly

Phase 2: Optional Type Hints (11 parameters)

• Adds proper Type | None syntax using Python 3.9+ union notation
• Covers str, bool, int, and list types where None has semantic meaning

All changed parameters:

• pythainlp.summarize.mt5.mT5Summarizer.__init__(pretrained_mt5_model_name) - converted to str = ""
• pythainlp.generate.wangchanglm.WangChanGLM.instruct_generate(context) - converted to str = ""
• pythainlp.classify.param_free.GzipModel.__init__(model_path) - converted to str = ""
• pythainlp.classify.param_free.GzipModel.__init__(training_data) - converted to list[tuple[str, str]] | None
• pythainlp.corpus.core.get_hf_hub(filename) - converted to str = ""
• pythainlp.transliterate.wunsen.WunsenTransliterate.transliterate(jp_input, zh_sandhi, system) - 3 params with Optional
• pythainlp.util.date.thai_strptime(add_year) - converted to int | None
• pythainlp.augment.wordnet.WordNetAug.find_synonyms(pos) - converted to str | None
• pythainlp.corpus.wordnet - 5 functions (synsets, all_lemma_names, all_synsets, lemmas, morphy) with pos: str | None

Example:

# Phase 1: Empty string conversion
# Before
def __init__(self, model_path: str = None):
    if model_path is not None:
        self.load(model_path)

# After
def __init__(self, model_path: str = ""):
    if model_path:
        self.load(model_path)

# Phase 2: Optional type hints
# Before
def synsets(word: str, pos: str = None, lang: str = "tha"):
    return wordnet.synsets(lemma=word, pos=pos, lang=lang)

# After
def synsets(word: str, pos: str | None = None, lang: str = "tha"):
    return wordnet.synsets(lemma=word, pos=pos, lang=lang)

What was wrong

Type hints specified concrete types (e.g., str, int, bool, list) but defaults were None, creating type inconsistency. Python 3.9+ supports proper type annotations; using None for optional parameters requires Type | None union syntax.

How this fixes it

• Phase 1: Changes defaults from None to "" where semantically appropriate (empty string is equivalent to None)
• Phase 2: Adds proper Type | None union syntax for parameters where None has distinct semantic meaning
• Updates conditional checks: is None → not x, is not None → if x, in (None, "") → not x
• Updates all docstrings to document default values
• Uses Python 3.9+ union syntax (Type | None) as all files have from __future__ import annotations

Fully backward compatible: empty string evaluates to False identically to None, and Optional type hints don't change runtime behavior.

Your checklist for this pull request

• Passed code styles and structures
• Passed code linting checks and unit test

Original prompt

Fix inappropriate use of "str = None" defaults in function parameters.

• Scan the codebase and find the inappropriate use of defaults that do not match the type of parameter
• Use str = "" instead of str = None when possible. In that case, recheck relevant values in the function. Adjust comparison accordingly. For example, replace "if x is not None" with "if x" as appropriate.
• Target Python version is 3.9

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

[coveralls]

coverage: 52.791% (-0.09%) from 52.878%
when pulling e796081 on copilot/fix-str-default-parameter-usage
into da8c3b6 on dev.

[bact]

@copilot check further to other cases of None defaults that do not match type hints. Convert them to Optional[] when possible. Test if results are the same. Update docstring. Target Python 3.9, with future imports.

[Copilot]

@copilot check further to other cases of None defaults that do not match type hints. Convert them to Optional[] when possible. Test if results are the same. Update docstring. Target Python 3.9, with f...

Done! Converted all None defaults that don't match type hints to use Optional[] with Python 3.9+ union syntax (Type | None).

Fixed in commits:

• 7e77fe2: Added Optional type hints for 10 parameters across 4 files (transliterate/wunsen.py, util/date.py, augment/wordnet.py, corpus/wordnet.py)
• e7f140a: Fixed training_data list type hint in classify/param_free.py

All docstrings updated to document default values. Tested thai_strptime to confirm behavior unchanged. No remaining type mismatches found in codebase.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud