function isNullOrUndefined(scope, node) {
	return (
		isNullLiteral(node) ||
		(node.type === "Identifier" &&
			node.name === "undefined" &&
			isReferenceToGlobalVariable(scope, node)) ||
		(node.type === "UnaryExpression" && node.operator === "void")
	);
}
Checks whether or not a node is `null` or `undefined`. Similar to the one
found in ast-utils.js, but this one correctly handles the edge case that
`undefined` has been redefined.
@param {Scope} scope Scope in which the expression was found.
@param {ASTNode} node A node to check.
@returns {boolean} Whether or not the node is a `null` or `undefined`.
@public