presto-geospatial/src/main/java/io/prestosql/plugin/geospatial/GeoFunctions.java/GeoFunctions/stExteriorRing
class GeoFunctions:    @SqlNullable
    @Description("Returns a line string representing the exterior ring of the POLYGON")
    @ScalarFunction("ST_ExteriorRing")
    @SqlType(GEOMETRY_TYPE_NAME)
    public static Slice stExteriorRing(@SqlType(GEOMETRY_TYPE_NAME) Slice input)
    {
        OGCGeometry geometry = deserialize(input);
        validateType("ST_ExteriorRing", geometry, EnumSet.of(POLYGON));
        if (geometry.isEmpty()) {
            return null;
        }
        return serialize(((OGCPolygon) geometry).exteriorRing());
    }