fix: treat empty property strings as present in helpers

[daviddallakyan2005]

Closes #3713

Rationale for this change

property_as_int, property_as_float, and get_first_property_value used a truthy walrus check (if value := properties.get(...)). An empty string is falsy in Python, so a present "" was treated as a missing key: the typed helpers returned the default instead of parsing, and get_first_property_value skipped to the next name.

This is the same class of bug as #3660 (falsy 0 collapsed to unset) and #3745 (CLI property lookup reported "" as missing). These helpers now use is not None, matching those PRs and the typed getters already in Config.get_int / get_bool. A missing key still returns the default. A present empty string is a value: int and float properties raise ValueError (same as any other unparseable string), and get_first_property_value returns "".

property_as_bool keeps the empty-string fallback behavior added on main in #3492.

Other walrus .get sites (IO, catalog, table locations/metadata) are left for follow-ups.

Are these changes tested?

Yes. Regression tests cover empty strings for int and float properties and for get_first_property_value, while preserving the boolean fallback from #3492.

• make lint
• make test → 3933 passed, 3 skipped, 1569 deselected
• uv run pytest tests/utils/test_properties.py -v → 14 passed after resolving the conflict

Are there any user-facing changes?

Yes. An explicitly empty int or float property now raises ValueError instead of silently using the default, and get_first_property_value no longer skips an empty string. Changelog label requested.

[Fokko]

Thanks for raising this PR @daviddallakyan2005. I think this one is debatable. What's the added value of having an empty string? I think unsetting the property is the right thing to do.

[daviddallakyan2005]

That makes sense, thanks. Looking at it again, I agree that an empty string is not useful for typed properties. Unlike 0 in #3660, it is not a valid value, so unsetting the property is clearer.

I also noticed that get_first_property_value is mainly used for AWS credential and region fallbacks. Returning an empty string could prevent a valid fallback from being used.

I can close this PR, or change the checks to be more explicit without changing the current behavior. Which would you prefer?

[daviddallakyan2005]

The integration-test failure on this PR is the same as main. #3476 calls deprecated PuffinFile.to_vector(), and warnings are errors. I opened #3803 and #3804 to update that test. It is unrelated to the empty-property change here.

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