Incorrect simplification with in operator involved

[sb98052]

(function () {
  let n = __abstract({x:1}, "o");
  let s;

  if (n!==undefined) {
    s = 'foobar' in n;
  }

  global.s = s;
})();

prepacks to:

(function () {
  var _$0 = this;

  _$0.s = true;
}).call(this);

[sb98052]

This is fine. The way the object n is declared sets the values domain to a singleton with that object.