toJson method
Creates a json from the object
Implementation
Map toJson() {
return {
'location': location,
'title': title,
'address': address,
'foursquare_id': foursquareId,
'foursquare_type': foursquareType,
'google_place_id': googlePlaceId,
'google_place_type': googlePlaceType,
}..removeWhere((_, v) => v == null);
}