workspace and parent params needed for move endpoint + root is same as parent_id is None/null

tracim/models/context_models.py

     @property
     def parent_id(self) -> int:
         """
-        Return parent_id of the content, if it doesn't exist return 0
+        Return parent_id of the content
         """
-        if not self.content.parent_id:
-            return 0
         return self.content.parent_id
 
     @property

tracim/tests/functional/test_workspaces.py

         )
         params = {
             'new_parent_id': '4',  # Salads
+            'new_workspace_id': '2',
         }
         params_folder1 = {
             'parent_id': 3,
             )
         )
         params = {
-            'new_parent_id': '0',  # root
+            'new_parent_id': None,  # root
+            'new_workspace_id': 2,
         }
         params_folder1 = {
             'parent_id': 3,
         assert not [content for content in new_folder1_contents if content['content_id'] == 8]  # nopep8
         assert [content for content in new_folder2_contents if content['content_id'] == 8]  # nopep8
         assert res.json_body
-        assert res.json_body['parent_id'] == 0
+        assert res.json_body['parent_id'] is None
         assert res.json_body['content_id'] == 8
         assert res.json_body['workspace_id'] == 2
 
         )
         params = {
             'new_parent_id': '2',  # Menus
+            'new_workspace_id': '1',
         }
         params_folder1 = {
             'parent_id': 3,
             )
         )
         params = {
-            'new_parent_id': '0', # root
+            'new_parent_id': None,  # root
             'new_workspace_id': '1',
         }
         params_folder1 = {
         assert not [content for content in new_folder1_contents if content['content_id'] == 8]  # nopep8
         assert [content for content in new_folder2_contents if content['content_id'] == 8]  # nopep8
         assert res.json_body
-        assert res.json_body['parent_id'] == 0
+        assert res.json_body['parent_id'] is None
         assert res.json_body['content_id'] == 8
         assert res.json_body['workspace_id'] == 1
 

tracim/views/core_api/schemas.py

     # (the user must be content manager of both workspaces)
     new_parent_id = marshmallow.fields.Int(
         example=42,
-        description='id of the new parent content id.'
+        description='id of the new parent content id.',
+        allow_none=True,
+        required=True,
     )
     new_workspace_id = marshmallow.fields.Int(
         example=2,
         description='id of the new workspace id.',
-        allow_none=True,
-        default=None,
+        required=True
     )
 
     @post_load