DynamicGeoJsonBaseField for shapely.geometry

I was trying to directly store shapely.geometry.multipolygon.MultiPolygon and shapely.geometry.polygon.Polygon. I ended up creating a DynamicGeoJsonBaseField.
This is my first time here not sure how I can contribute to this amazing community.

class DynamicGeoJsonBaseField(GeoJsonBaseField):

def validate(self, value):
    if not isinstance(value, BaseGeometry):
        self.error(f'{self.name} is not a BaseGeometry')
    if 

def to_mongo(self, value):

    dict_mongo_geo_json = {}
    dict_mongo_geo_json['type'] = value.geometryType()
    coordinates = []
    if isinstance(value, Polygon):
        coordinates = list(value.exterior.coords)
    elif isinstance(value, MultiPolygon):
        coordinates = [list(i.exterior.coords) for i in list(value)]
    dict_mongo_geo_json['coordinates'] = coordinates
    return super().to_mongo(dict_mongo_geo_json)

Start with GeoJsonBaseField and the provided DynamicGeoJsonBaseField example. The issue names no repository file or test; done would be agreed support for directly storing Polygon and MultiPolygon values, with corresponding tests identified during investigation.