geoPHP pointOnSurface always returns null

Question

Using geoPHP with geos installed. pointOnSurface() for a valid polygon always returns null. While other functions such as centroid() work fine.

Example:

geoPHP::geosInstalled();          //true

$geo->geometryType();             //Polygon

$point = $geo->centroid();        //Point {coords: [-73.931519444925, 40.85512387767]}

$geo->covers($point);             //true

$geo->pointOnSurface();           //null

I'm wondering if anyone else has this problem (or I'm missing something)?

Edit: This workaround seems to do the trick:

$geos_geometry = $geo->geos();                    //GEOSGeometry

$geos_POS = $geos_geometry->pointOnSurface();     //GEOSGeometry

$geos_POS->isEmpty();                             //false

$geos_POS->getX();                                //-73.932666589981

$geos_POS->getY();                                //40.85405746088