Task: Add modern Python type hints to the following code. Follow these rules:

1. Annotate all function parameters and return types
2. Use built-in generics (e.g., list[str] not List[str])
3. Use | for unions instead of Union (Python 3.10+ style)
4. Add -> None for void returns
5. Import required types ONLY when needed
6. Preserve original functionality exactly
7. For ambiguous types, use:
   • Any for completely unknown types
   • TypeVar for generic relationships
   • Comments # type: ignore for unresolvable cases

Examples:

Example 1: Simple function

# BEFORE
def greet(name):
    return "Hello " + name

# AFTER
def greet(name: str) -> str:
    return "Hello " + name

Example 2: Container types

# BEFORE
def process_items(items, default=None):
    return [item.upper() for item in items] + [default]

# AFTER
def process_items(items: list[str], default: str | None = None) -> list[str | None]:
    return [item.upper() for item in items] + [default]