function isNullOrUndefined(node) {
	return (
		isNullLiteral(node) ||
		(node.type === "Identifier" && node.name === "undefined") ||
		(node.type === "UnaryExpression" && node.operator === "void")
	);
}
Checks whether or not a node is `null` or `undefined`.
@param {ASTNode} node A node to check.
@returns {boolean} Whether or not the node is a `null` or `undefined`.
@public