anchor.diff:  }) ->
       Fields = lists:foldl(fun
           (<<"onedata_keyvalue">>, Acc) ->
  -            KeyValues = case maps:without(?ONEDATA_ATTRS, Metadata) of
  +            KeyValues = case maps:without(?ONEDATA_SPECIAL_XATTRS, Metadata) of
                   Map when map_size(Map) == 0 -> null;
                   Map -> Map
               end,
  
positive.code:     Exists = lists:foldl(fun
          (<<"onedata_keyvalue">>, Acc) ->
              Acc#{<<"onedata_keyvalue">> => map_size(
                  maps:without(?ONEDATA_ATTRS, Metadata)) > 0
              };
          (FieldName, Acc) ->
              Acc#{FieldName => maps:is_key(FieldName, Metadata)}
  
negative.code: %%% seq: 100
  %%% fileMeta:
  %%%     rev: 2-c500a5eb026d9474429903d47841f9c5
  %%%     mutators: ["p1.1542789098.test"]
  %%%     changed: true
  %%%     deleted: false
  %%%     fields:
  %%%         owner: john
  %%% customMetadata:
  %%%     rev: 1-09f941b4e8452ef6a244c5181d894814
  %%%     mutators: ["p1.1542789098.test"]
  %%%     changed: false
  %%%     deleted: false
  %%%     exists:
  %%%         onedata_rdf: true
  %%%     fields:
  %%%         onedata_json:
  %%%             name1: value1
  %%%             name2: value2
  %%%
  %%% @end
  %%%--------------------------------------------------------------------
  