Fix mutable default arguments across function signatures

[Copilot]

Python's mutable default arguments are evaluated once at function definition and shared across all calls, causing unintended state pollution. Seven functions used dict = {} as defaults.

Changes

• wrangles/utils.py: evaluate_conditional(), safe_str_transform()
• wrangles/recipe_wrangles/split.py: dictionary()
• wrangles/recipe_wrangles/convert.py: _getSentenceCase()
• wrangles/connectors/test.py: read()
• wrangles/connectors/train.py: lookup.write()
• wrangles/connectors/mongodb.py: read()

Pattern Applied

# Before
def read(rows: int, values: dict = {}) -> pd.DataFrame:
    data = {}
    for key, val in values.items():
        data[key] = generate_values(val, rows)
    return pd.DataFrame(data)

# After
def read(rows: int, values: dict = None) -> pd.DataFrame:
    if values is None:
        values = {}
    data = {}
    for key, val in values.items():
        data[key] = generate_values(val, rows)
    return pd.DataFrame(data)

Each function now uses None as default with explicit initialization, preventing cross-call state leakage.

Original prompt

please work on issue 796 (dictioanry defaults)

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