import re


def strings_or_none_in_brackets(string):
    """Returns a string found in brackets or none if not found.

    Args:
        string: An input string.

    Returns:
        A string found in brackets or none if not found. For example:

        input : hello [{window}],
        output : {window}
    """
    result_or_none = re.findall(r"\[([A-Za-z0-9_]+)\]", string)
    if result_or_none is not None:
        return result_or_none
    else:
        return None