FURB168 has false positives on empty tuples

[dscorbett]

Summary

isinstance-type-none (FURB168) has false positives when the tuples it checks are empty. () is not the same as None.

Playground

$ cat >furb168.py <<'# EOF'
from typing import Union
print(isinstance(None, ()))
try:
    print(isinstance(None, Union[()]))
except TypeError as e:
    print(f"{type(e).__name__}: {e}")
# EOF

$ python furb168.py
False
TypeError: Cannot take a Union of no types.

$ ruff --isolated check furb168.py --select FURB168 --fix
Found 2 errors (2 fixed, 0 remaining).

$ cat furb168.py
from typing import Union
print((None is None))
try:
    print((None is None))
except TypeError as e:
    print(f"{type(e).__name__}: {e}")

$ python furb168.py
True
True

Version

ruff 0.12.1 (32c5418 2025-06-26)

[MeGaGiGaGon]

I think I found the source of the issue:

ruff/crates/ruff_linter/src/rules/refurb/rules/isinstance_type_none.rs

Lines 102 to 104 in 34052a1

	// Ex) `(type(None),)`
	Expr::Tuple(tuple) => tuple.iter().all(|element| inner(element, false, semantic)),

The all of an empty iterable is true, so is_none returns true on an empty tuple.