test Model: char fields should be nullable

EditorialModel/test/me.json

   "string": "{\"fre\": \"Personnes\"}"
  },
  "4": {
-  "nullable": false,
+  "nullable": true,
   "date_update": "Fri Oct 16 11:05:04 2015",
   "optional": false,
   "icon": "0",
   "sortcolumn": "rank"
  },
  "7": {
-  "nullable": false,
+  "nullable": true,
   "date_update": "Fri Oct 16 11:05:04 2015",
   "optional": true,
   "icon": "0",
   "name": "soustitre"
  },
  "9": {
-  "nullable": false,
+  "nullable": true,
   "date_update": "Fri Oct 16 11:05:04 2015",
   "optional": false,
   "icon": "0",
   "name": "nom"
  },
  "10": {
-  "nullable": false,
+  "nullable": true,
   "date_update": "Fri Oct 16 11:05:04 2015",
   "optional": true,
   "icon": "0",
   "name": "prenom"
  },
  "11": {
-  "nullable": false,
+  "nullable": true,
   "date_update": "Fri Oct 16 11:05:04 2015",
   "optional": false,
   "icon": "0",
   "name": "auteur"
  },
  "12": {
-  "nullable": false,
+  "nullable": true,
   "date_update": "Fri Oct 16 11:05:04 2015",
   "optional": false,
   "icon": "0",
   "sortcolumn": "rank"
  },
  "16": {
-  "nullable": false,
+  "nullable": true,
   "date_update": "Fri Oct 16 11:05:04 2015",
   "optional": false,
   "icon": "0",
   "name": "titre"
  },
  "18": {
-  "nullable": false,
+  "nullable": true,
   "date_update": "Fri Oct 16 11:05:04 2015",
   "optional": true,
   "icon": "0",
   "sortcolumn": "rank"
  },
  "21": {
-  "nullable": false,
+  "nullable": true,
   "date_update": "Fri Oct 16 11:05:04 2015",
   "optional": true,
   "icon": "0",
   "name": "class_id"
  },
  "24": {
-  "nullable": false,
+  "nullable": true,
   "date_update": "Fri Oct 16 11:05:04 2015",
   "max_length": 128,
   "icon": "0",
   "name": "class_id"
  },
  "29": {
-  "nullable": false,
+  "nullable": true,
   "date_update": "Fri Oct 16 11:05:04 2015",
   "max_length": 128,
   "icon": "0",
   "name": "class_id"
  },
  "34": {
-  "nullable": false,
+  "nullable": true,
   "date_update": "Fri Oct 16 11:05:04 2015",
   "max_length": 128,
   "icon": "0",