public LineStringExpression<?> exteriorRing() {
        if (exterorRing == null) {
            exterorRing = GeometryExpressions.lineStringOperation(SpatialOps.EXTERIOR_RING, mixin);
        }
        return exterorRing;
    }
Returns the exterior ring of this Polygon.

@return exterior ring
querydsl-spatial/src/main/java/com/querydsl/spatial/PolygonExpression.java