from __future__ import annotations
from datetime import date
from typing import List, Optional

def csv_to_list(s: Optional[str]) -> List[str]:
    return [x.strip() for x in (s or "").split(",") if x.strip()]

def list_to_csv(items: List[str]) -> str:
    return ", ".join([i.strip() for i in items if i.strip()])

def calc_age(born: Optional[date]) -> Optional[int]:
    if not born:
        return None
    today = date.today()
    return today.year - born.year - ((today.month, today.day) < (born.month, born.day))