code: function isNullOrUndefined(node) {
      return (
          module.exports.isNullLiteral(node) ||
          (node.type === "Identifier" && node.name === "undefined") ||
          (node.type === "UnaryExpression" && node.operator === "void")
      );
  }
docs: 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