- 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'