from typing import List
from typing import Optional


def str_replace(s: str, old: List[str], new: Optional[List[str]] = None) -> str:
    """Replaces occurences of all strings in *old* by the corresponding ones in *new*.
    If None is passed in new, *old* are simply removed fromm *s*"""
    if new is None: new = [''] * len(old)
    for o, n in zip(old, new):
        s = s.replace(o, n)
    return s