from typing import Union
from typing import List


def append_forward_slash_path(
    paths: Union[List[str], str]
) -> Union[List[str], str, None]:
    """
    Returns the input string(s), in the same format as they were passed in, with a minimum of one forward slash
    at the end, given that no forward slash exists at the end.

    :param paths: one or more paths to add a forward slash to.
    :return:
    """
    if paths is None:
        return None
    if isinstance(paths, str):
        if paths[-1] != "/":
            paths += "/"
        return paths
    else:
        output = [path + ("/" if path[-1] != "/" else "") for path in paths]
        return output