anchor.diff:  -spec get_xattr_metadata(file_meta:uuid(), xattr:name()) ->
       {ok, xattr:value()} | datastore:get_error().
   get_xattr_metadata(FileUuid, Name) ->
  -    case custom_metadata:get(FileUuid) of
  +    case get(FileUuid) of
           {ok, #document{value = #custom_metadata{value = Meta}}} ->
               case maps:get(Name, Meta, undefined) of
                   undefined ->
  
positive.code: -spec get_json_metadata(file_meta:uuid(), [binary()]) ->
      {ok, #{}} | datastore:get_error().
  get_json_metadata(FileUuid, Names) ->
      case custom_metadata:get(FileUuid) of
          {ok, #document{value = #custom_metadata{value = Meta}}} ->
              Json = maps:get(?JSON_PREFIX, Meta, #{}),
              {ok, custom_meta_manipulation:find(Json, Names)};
  
negative.code: -spec set_json_metadata(file_meta:uuid(), #{}, [binary()]) ->
      {ok, file_meta:uuid()} | datastore:get_error().
  set_json_metadata(FileUuid, JsonToInsert, Names) ->
      case get(FileUuid) of %todo use create or update
          {ok, Doc = #document{value = Meta = #custom_metadata{value = MetaValue}}} ->
              Json = maps:get(?JSON_PREFIX, MetaValue, #{}),
              NewJson = custom_meta_manipulation:insert(Json, JsonToInsert, Names),
  