At least the Python bind of GraphCutSeamFinders find() method returns -> None.

Graph Cut Seam finding was therefore removed from stitching_detailed.py in dbd65a3.

However, on the long run, GraphCutSeamFinder should return the respective masks and also be integrated into stitching_detailed.py again.

In comparison, DpSeamFinders find() does not state any return values, however it implements SeamFinder and hence it's find() method, which returns -> masks

Detail:

I looked into the code and also noticed that GraphCutSeamFinder is not even a valid entry of createDefault():

Ptr<SeamFinder> SeamFinder::createDefault(int type)
{
    if (type == NO)
        return makePtr<NoSeamFinder>();
    if (type == VORONOI_SEAM)
        return makePtr<VoronoiSeamFinder>();
    if (type == DP_SEAM)
        return makePtr<DpSeamFinder>();
    CV_Error(Error::StsBadArg, "unsupported seam finder method");
}

Is this intentional behavior?
GraphCutSeamFinder is the only Finder which is defined explicitly as class (line 1108), while the others are pointers.