anchor.diff:  %%--------------------------------------------------------------------
   %% @private
   %% @doc
  -%% Checks whether provider with given domain exists.
  +%% Checks whether provider with given domain exists. If yes, returns its id.
   %% @end
   %%--------------------------------------------------------------------
   -spec is_domain_occupied(Domain :: binary()) ->
       {true, ProviderId :: od_provider:id()} | false.
   is_domain_occupied(Domain) ->
       {ok, Providers} = od_provider:list(),
  -    case [P#document.key ||
  -        P <- Providers, P#document.value#od_provider.domain == Domain] of
  -        % multiple results should not happen, but older versions did not enforce
  +    MatchingIds = [P#document.key ||
  +        P <- Providers, P#document.value#od_provider.domain == Domain],
  +    case MatchingIds of
  +        % multiple results should not happen but older versions did not enforce
           % unique domains
           [Id | _] -> {true, Id};
           [] -> false
  
positive.code: -spec update_provider_domain(ProviderId :: od_provider:id(),
      Data :: entity_logic:data()) -> entity_logic:update_result().
  update_provider_domain(ProviderId, Data) ->
      dns_state:remove_delegation_config(ProviderId),
      Domain = maps:get(<<"domain">>, Data),
      Result = critical_section:run({domain_config, Domain}, fun() ->
          case is_domain_occupied(Domain) of
  
negative.code:         end
      end),
      case Result of
          {ok, _} ->
              dns_state:remove_delegation_config(ProviderId),
              ok;
          Error -> Error
      end.
  
  