Java Streams - Sort if Comparator exists

I have a class where optionally a Comparator can be specified.

Since the Comparator is optional, I have to evaluate its presence and execute the same stream code, either with sorted() or without:

if(comparator != null) {
    [...].stream().map()[...].sorted(comparator)[...];
} else {
    [...].stream().map()[...];
}

Question:
Is there a more elegant way to do this without the code duplication?

Note:
A default Comparator is not an option, I just want to keep the original order of the values I am streaming.

Besides, the elements are already mapped at the point of sorting, so I can not somehow reference the root list of the stream, as I do not have the original elements anymore.