from typing import List


def str_in_list_to_lower(list_of_strings: List[str]) -> List[str]:
    """
    >>> str_in_list_to_lower(['A','b','C'])
    ['a', 'b', 'c']
    >>> str_in_list_to_lower([])
    []

    """
    if not list_of_strings:
        return list_of_strings

    return [string.lower() for string in list_of_strings]