This is an extremely common pattern used in cjs modules. rollup-plugin-commonjs currently creates suboptimal code for that, see the example from zloirock/core-js#125 (comment):

var exports$198 = {};
var module$198 = { 'exports': exports$198 };
module$198.exports = require$$0$5.document && document.documentElement;

// OR

var exports$129 = {};
var module$129 = { 'exports': exports$129 };
module$129.exports = function(it){
  return typeof it === 'object' ? it !== null : typeof it === 'function';
};

If rollup-plugin-commonjs were a little bit smarter, it could avoid allocating the unused exports var/object in that case.
It it were even smarter, it may also be possible to avoid the modules map too, but I guess that would depend on the importer side, so it might not be feasible.