def make_string(arg):
    """Used to overload Dunder method __str__ of any class
    This is used to convert <class 'class_name'> to string form and this is also a valid json
    :param arg: arg ~ self, iterate over it and form key-value {attribute: value}
    :return: string value of self(arg) of any class
    """
    res = str()
    is_first = True
    for k, v in arg.__dict__.items():
        if v is not None and v is not '':
            if not is_first:
                res += ','
            if v.__str__()[0] == '{' or v.__str__()[0] == '[':
                res += '"{}":{}'.format(k, v)
            else:
                res += '"{}":"{}"'.format(k, v)
            is_first = False
    if is_first:
        return None
    return '{' + res + '}'
