Test and fix all possible cases of champ carte serialization

app/models/champs/carte_champ.rb

@@ -51,7 +51,7 @@ class Champs::CarteChamp < Champ
     # We used to store in the value column a json array with coordinates.
     if geo_json.is_a?(Array)
       # If it is a coordinates array, format it as a GEO-JSON
-      GeojsonService.to_json_polygon_for_selection_utilisateur(geo_json)
+      JSON.parse(GeojsonService.to_json_polygon_for_selection_utilisateur(geo_json))
     else
       # It is already a GEO-JSON
       geo_json

app/serializers/champ_serializer.rb

@@ -12,11 +12,9 @@ class ChampSerializer < ActiveModel::Serializer
   def value
     case object
     when GeoArea
-      object.geometry
+      object.geometry.to_json
     when Champs::CarteChamp
-      if object.value.present?
-        JSON.parse(object.value)
-      end
+      object.user_geometry.to_json
     when Champs::DecimalNumberChamp
       if object.value.present?
         object.value.to_f
@@ -71,7 +69,7 @@ class ChampSerializer < ActiveModel::Serializer
       libelle: legacy_carto_libelle,
       type_champ: legacy_carto_type_champ,
       order_place: -1,
-      descripton: ''
+      description: ''
     }
   end