Compiler believes variable can be undefined in map

Given an array `foo` and a variable `bar` of type `{!Object|undefined}`, the following code

``` javascript
doSomething() {
if (!bar) {
return;
}

return foo.map(element => transform(element, bar));
}

/**
* @param {!Object}
*/
transform(element, bar) {
return ...;
}
```

Fails compilation because closure compiler insists that `bar` can not be passed to `transform` because it may be `undefined`, which is obviously not the case / impossible.