How to use the libcst._maybe_sentinel.MaybeSentinel.DEFAULT function in libcst

config: ParserConfig,
    children: typing.Sequence[typing.Any],
    single_child_is_sequence: bool,
    sequence_type: typing.Union[
        typing.Type[Tuple], typing.Type[List], typing.Type[Set]
    ],
) -> typing.Any:
    if not single_child_is_sequence and len(children) == 1:
        return children[0]
    # N.B. The parent node (e.g. atom) is responsible for computing and attaching
    # whitespace information on any parenthesis, square brackets, or curly braces
    elements = []
    for wrapped_expr_or_starred_element, comma_token in grouper(children, 2):
        expr_or_starred_element = wrapped_expr_or_starred_element.value
        if comma_token is None:
            comma = MaybeSentinel.DEFAULT
        else:
            comma = Comma(
                whitespace_before=parse_parenthesizable_whitespace(
                    config, comma_token.whitespace_before
                ),
                # Only compute whitespace_after if we're not a trailing comma.
                # If we're a trailing comma, that whitespace should be consumed by the
                # TrailingWhitespace, parenthesis, etc.
                whitespace_after=(
                    parse_parenthesizable_whitespace(
                        config, comma_token.whitespace_after
                    )
                    if comma_token is not children[-1]
                    else SimpleWhitespace("")
                ),
            )

This supports named keyword arguments in the form of ``keyword=value`` and variable
    argument expansion using ``*args`` or ``**kwargs`` syntax.
    """

    #: The argument expression itself, not including a preceding keyword, or any of
    #: the surrounding the value, like a comma or asterisks.
    value: BaseExpression

    #: Optional keyword for the argument.
    keyword: Optional[Name] = None

    #: The equals sign used to denote assignment if there is a keyword.
    equal: Union[AssignEqual, MaybeSentinel] = MaybeSentinel.DEFAULT

    #: Any trailing comma.
    comma: Union[Comma, MaybeSentinel] = MaybeSentinel.DEFAULT

    #: A string with zero, one, or two asterisks appearing before the name. These are
    #: expanded into variable number of positional or keyword arguments.
    star: Literal["", "*", "**"] = ""

    #: Whitespace after the ``star`` (if it exists), but before the ``keyword`` or
    #: ``value`` (if no keyword is provided).
    whitespace_after_star: BaseParenthesizableWhitespace = SimpleWhitespace.field("")
    #: Whitespace after this entire node. The :class:`Comma` node (if it exists) may
    #: also store some trailing whitespace.
    whitespace_after_arg: BaseParenthesizableWhitespace = SimpleWhitespace.field("")

    def _validate(self) -> None:
        if self.keyword is None and isinstance(self.equal, AssignEqual):
            raise CSTValidationError(
                "Must have a keyword when specifying an AssignEqual."

"""

    #: The lower bound in the slice, if present
    lower: Optional[BaseExpression]

    #: The upper bound in the slice, if present
    upper: Optional[BaseExpression]

    #: The step in the slice, if present
    step: Optional[BaseExpression] = None

    #: The first slice operator
    first_colon: Colon = Colon.field()

    #: The second slice operator, usually omitted
    second_colon: Union[Colon, MaybeSentinel] = MaybeSentinel.DEFAULT

    def _visit_and_replace_children(self, visitor: CSTVisitorT) -> "Slice":
        return Slice(
            lower=visit_optional(self, "lower", self.lower, visitor),
            first_colon=visit_required(self, "first_colon", self.first_colon, visitor),
            upper=visit_optional(self, "upper", self.upper, visitor),
            second_colon=visit_sentinel(
                self, "second_colon", self.second_colon, visitor
            ),
            step=visit_optional(self, "step", self.step, visitor),
        )

    def _codegen_impl(self, state: CodegenState) -> None:
        lower = self.lower
        if lower is not None:
            lower._codegen(state)

@add_slots
@dataclass(frozen=True)
class From(CSTNode):
    """
    A ``from x`` stanza in a :class:`Yield` or :class:`Raise`.
    """

    #: The expression that we are yielding/raising from.
    item: BaseExpression

    #: The whitespace at the very start of this node.
    whitespace_before_from: Union[
        BaseParenthesizableWhitespace, MaybeSentinel
    ] = MaybeSentinel.DEFAULT

    #: The whitespace after the ``from`` keyword, but before the ``item``.
    whitespace_after_from: BaseParenthesizableWhitespace = SimpleWhitespace.field(" ")

    def _validate(self) -> None:
        if (
            isinstance(self.whitespace_after_from, BaseParenthesizableWhitespace)
            and self.whitespace_after_from.empty
            and not self.item._safe_to_use_with_word_operator(ExpressionPosition.RIGHT)
        ):
            raise CSTValidationError(
                "Must have at least one space after 'from' keyword."
            )

    def _visit_and_replace_children(self, visitor: CSTVisitorT) -> "From":
        return From(

"""
    A single argument to a :class:`Call`.

    This supports named keyword arguments in the form of ``keyword=value`` and variable
    argument expansion using ``*args`` or ``**kwargs`` syntax.
    """

    #: The argument expression itself, not including a preceding keyword, or any of
    #: the surrounding the value, like a comma or asterisks.
    value: BaseExpression

    #: Optional keyword for the argument.
    keyword: Optional[Name] = None

    #: The equals sign used to denote assignment if there is a keyword.
    equal: Union[AssignEqual, MaybeSentinel] = MaybeSentinel.DEFAULT

    #: Any trailing comma.
    comma: Union[Comma, MaybeSentinel] = MaybeSentinel.DEFAULT

    #: A string with zero, one, or two asterisks appearing before the name. These are
    #: expanded into variable number of positional or keyword arguments.
    star: Literal["", "*", "**"] = ""

    #: Whitespace after the ``star`` (if it exists), but before the ``keyword`` or
    #: ``value`` (if no keyword is provided).
    whitespace_after_star: BaseParenthesizableWhitespace = SimpleWhitespace.field("")
    #: Whitespace after this entire node. The :class:`Comma` node (if it exists) may
    #: also store some trailing whitespace.
    whitespace_after_arg: BaseParenthesizableWhitespace = SimpleWhitespace.field("")

    def _validate(self) -> None:

def convert_decorator(config: ParserConfig, children: Sequence[Any]) -> Any:
    atsign, name, *arglist, newline = children
    if not arglist:
        # This is either a name or an attribute node, so just extract it.
        decoratornode = name
    else:
        # This needs to be converted into a call node, and we have the
        # arglist partial.
        lpar, *args, rpar = arglist
        args = args[0].args if args else []

        # If the trailing argument doesn't have a comma, then it owns the
        # trailing whitespace before the rpar. Otherwise, the comma owns
        # it.
        if len(args) > 0 and args[-1].comma == MaybeSentinel.DEFAULT:
            args[-1] = args[-1].with_changes(
                whitespace_after_arg=parse_parenthesizable_whitespace(
                    config, rpar.whitespace_before
                )
            )

        decoratornode = Call(
            func=name,
            whitespace_after_func=parse_simple_whitespace(
                config, lpar.whitespace_before
            ),
            whitespace_before_args=parse_parenthesizable_whitespace(
                config, lpar.whitespace_after
            ),
            args=tuple(args),
        )

def _validate(self) -> None:
        if len(self.names) == 0:
            raise CSTValidationError(
                "A Nonlocal statement must have at least one NameItem."
            )
        if self.names[-1].comma != MaybeSentinel.DEFAULT:
            raise CSTValidationError(
                "The last NameItem in a Nonlocal cannot have a trailing comma."
            )
        if self.whitespace_after_nonlocal.empty:
            raise CSTValidationError(
                "Must have at least one space after 'nonlocal' keyword."
            )

def convert_argslist(config: ParserConfig, children: Sequence[Any]) -> Any:
    params: List[Param] = []
    seen_default: bool = False
    star_arg: Union[Param, ParamStar, MaybeSentinel] = MaybeSentinel.DEFAULT
    kwonly_params: List[Param] = []
    star_kwarg: Optional[Param] = None

    def add_param(
        current_param: Optional[List[Param]], param: Union[Param, ParamStar]
    ) -> Optional[List[Param]]:
        nonlocal star_arg
        nonlocal star_kwarg
        nonlocal seen_default

        if isinstance(param, ParamStar):
            # Only can add this if we don't already have a "*" or a "*param".
            if current_param is params:
                star_arg = param
                current_param = kwonly_params
            else:

name: Name

    #: The class body.
    body: BaseSuite

    #: Sequence of base classes this class inherits from.
    bases: Sequence[Arg] = ()

    #: Sequence of keywords, such as "metaclass".
    keywords: Sequence[Arg] = ()

    #: Sequence of decorators applied to this class.
    decorators: Sequence[Decorator] = ()

    #: Optional open parenthesis used when there are bases or keywords.
    lpar: Union[LeftParen, MaybeSentinel] = MaybeSentinel.DEFAULT

    #: Optional close parenthesis used when there are bases or keywords.
    rpar: Union[RightParen, MaybeSentinel] = MaybeSentinel.DEFAULT

    #: Leading empty lines and comments before the first decorator. We
    #: assume any comments before the first decorator are owned by the
    #: class definition itself. If there are no decorators, this will
    #: still contain all of the empty lines and comments before the
    #: class definition.
    leading_lines: Sequence[EmptyLine] = ()

    #: Empty lines and comments between the final decorator and the
    #: :class:`ClassDef` node. In the case of no decorators, this will be empty.
    lines_after_decorators: Sequence[EmptyLine] = ()

    #: Whitespace after the ``class`` keyword and before the class name.