- Replace 'int | None' with 'Optional[int]' everywhere
- Replace 'subprocess.Popen | None' with 'Optional[subprocess.Popen]'
- Add Optional import to all affected files
- Update ruff target-version from py310 to py39
- The '|' syntax for Union types was introduced in Python 3.10 (PEP 604)
Fixes TypeError: unsupported operand type(s) for |: 'type' and 'NoneType'
677eb0bae3