anchor.diff:  -type change_req() :: #change_req{}.
   
   -define(DEFAULT_ALWAYS, false).
  --define(ONEDATA_ATTRS, [<<"onedata_json">>, <<"onedata_rdf">>]).
  +-define(ONEDATA_SPECIAL_XATTRS, [<<"onedata_json">>, <<"onedata_rdf">>]).
   
   
   %%%===================================================================
  
positive.code: %%% fields to return (`fields`), fields for which check existence
  %%% (`exists` - only possible for `customMetadata`),
  %%% whether information about this record should be send always or
  %%% on this record changes only (`always`).
  %%%
  %%% <record>:
  %%%     [fields: <fields>]
  
negative.code: }) ->
      Fields = lists:foldl(fun
          (<<"onedata_keyvalue">>, Acc) ->
              KeyValues = case maps:without(?ONEDATA_SPECIAL_XATTRS, Metadata) of
                  Map when map_size(Map) == 0 -> null;
                  Map -> Map
              end,
  