Bug in databricks.sql.exc.Error base class (#437)

[peco-engineer-bot]

Summary

Automated fix for #437 — Bug in databricks.sql.exc.Error base class.

In src/databricks/sql/exc.py, Error.str now returns self.message or "" (guaranteeing a str per Python's object.str contract cited in the issue) and message_with_context computes (self.message or "") + ": " + json.dumps(self.context, default=str), so a None message no longer raises TypeError: __str__ returned non-string or unsupported operand type(s) for +: 'NoneType' and 'str'. Both unit tests pass. This is a client-side exception-formatting artifact anchored in the Python data model (not end-to-end observable against a warehouse), so unit tests satisfy the offline carve-out.

Root cause & plan

Root cause: In src/databricks/sql/exc.py, the Error base class stores self.message = message (default None). __str__ returns self.message directly, so when message is None Python raises TypeError: __str__ returned non-string (type NoneType). Separately, message_with_context computes self.message + ": " + json.dumps(...), which raises TypeError: unsupported operand type(s) for +: 'NoneType' and 'str' when message is None. Both need to coerce/guard a None message. Correctness anchored in the Python data model (object.str must return a string), cited by the issue — a client-side artifact, not warehouse-observable, so unit tests satisfy the carve-out.
Files: src/databricks/sql/exc.py, tests/unit/test_exc.py
Planned coverage:

• Construct databricks.sql.exc.Error() with no message and assert str(e) returns a string (e.g. '') without raising TypeError — verifies str never returns non-string. (str returns None when message is None)
• Construct Error(context={...}) with message=None and assert message_with_context() returns a string containing the JSON-serialized context without raising TypeError. (message_with_context raises on None + str when message is None)

Files changed

• tests/unit/test_exc.py
• src/databricks/sql/exc.py

Test plan

• tests/unit/test_exc.py::TestError::test_str_returns_string_when_message_is_none — fails (red) against the original code, passes (green) after the fix
• tests/unit/test_exc.py::TestError::test_message_with_context_when_message_is_none — fails (red) against the original code, passes (green) after the fix

🤖 Generated by engineer-bot (bug-fix flow) — review before merge.

[peco-review-bot]

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