import re


def remove_white_characters(s):
    """
    Join the list of tokens and remove all white characters.

    Args:
        s (Union(list[str], str)): List of tokens

    Returns:
        str: String after removing white characters

    """
    if isinstance(s, list):
        s = ''.join(s)
    s = s.lower()
    s = re.sub(r'\s', '', s)
    return s