Any way to store empty polygon in Postgres?

[tec4]

Is there any way to store an empty polygon?

What I am trying to do is have a geometry column in Postgres that has a spatial index, so I cannot set the column to be nullable. In raw SQL, it would be something like this:

-- Create Dummy Table
CREATE TABLE poly_testing
(
    id SERIAL NOT NULL,
    poly geometry(Polygon,4326) NOT NULL,
    CONSTRAINT poly_testing_pkey PRIMARY KEY (id)
);

-- Insert empty polygon
insert into poly_testing (poly) 
values ('SRID=4326;POLYGON EMPTY')

I've tried to create an empty Polygon object by passing it no rings, like this but it fails:

    /**
     * @ORM\Column(name="poly", type="polygon", options={"srid": 4326})
     */
    protected ?Polygon $polygon = null;

    // ......

    $this->polygon = new Polygon([], 4326);

I get the following error:
Error: Method CrEOF\Spatial\PHP\Types\Geometry\Polygon::__toString() must return a string value

My Doctrine config looks like:

doctrine:
    dbal:
        driver: 'pdo_pgsql'
        server_version: '12.1'
        charset: utf8
        default_table_options:
            charset: utf8
            collate: utf8_unicode_ci
        url: '%env(resolve:DATABASE_URL)%'
        types:
            geometry:  CrEOF\Spatial\DBAL\Types\GeometryType
            point:         CrEOF\Spatial\DBAL\Types\Geometry\PointType
            polygon:    CrEOF\Spatial\DBAL\Types\Geometry\PolygonType

Any suggestions on how to go about storing an empty polygon or other geometry?

Thanks!