Better handle empty user selection layers

app/controllers/champs/carte_controller.rb

@@ -26,11 +26,11 @@ class Champs::CarteController < ApplicationController
     end
 
     geo_areas = []
-    geo_json = JSON.parse(geo_json)
+    geo_json = geo_json.blank? ? [] : JSON.parse(geo_json)
 
     if geo_json.first == ["error", "TooManyPolygons"]
       @error = true
-    else
+    elsif geo_json.present?
       if @champ.cadastres?
         cadastres = ModuleApiCartoService.generate_cadastre(geo_json)
         geo_areas += cadastres.map do |cadastre|

app/javascript/shared/carte.js

@@ -97,7 +97,9 @@ export function getCurrentMap(input) {
 export function addFreeDrawEvents(map, selector) {
   const input = findInput(selector);
   map.freeDraw.on('markers', ({ latLngs }) => {
-    if (polygonArea(latLngs) < 300000) {
+    if (latLngs.length === 0) {
+      input.value = '';
+    } else if (polygonArea(latLngs) < 300000) {
       input.value = JSON.stringify(latLngs);
     } else {
       input.value = '{ "error": "TooManyPolygons" }';

app/models/champ.rb

@@ -17,7 +17,16 @@ class Champ < ApplicationRecord
   end
 
   def mandatory_and_blank?
-    mandatory? && value.blank?
+    if mandatory?
+      case type_de_champ.type_champ
+      when TypeDeChamp.type_champs.fetch(:carte)
+        value.blank? || value == '[]'
+      else
+        value.blank?
+      end
+    else
+      false
+    end
   end
 
   def search_terms

spec/models/champ_shared_example.rb

@@ -9,6 +9,12 @@ shared_examples 'champ_spec' do
       it { expect(champ.mandatory_and_blank?).to be(true) }
     end
 
+    context 'when carte mandatory and blank' do
+      let(:type_de_champ) { build(:type_de_champ_carte, mandatory: mandatory) }
+      let(:value) { '[]' }
+      it { expect(champ.mandatory_and_blank?).to be(true) }
+    end
+
     context 'when not blank' do
       let(:value) { 'yop' }
       it { expect(champ.mandatory_and_blank?).to be(false) }