anchor.diff:              };
           (Key, Value) -> #{Key => Value}
       end, Params),
  -    filter_fields(expected_user_ctx_params(HelperName), Transformed);
  +    Ctx2 = case Ctx of
  +        #{<<"credentialsType">> := <<"none">>} ->
  +            Ctx#{<<"credentials">> => <<>>};
  +        _ -> Ctx
  +    end,
  +    filter_fields(expected_user_ctx_params(HelperName), Ctx2);
   
   prepare_user_ctx_params(HelperName, Params) ->
       filter_fields(expected_user_ctx_params(HelperName), Params).
  
positive.code: %%--------------------------------------------------------------------
  -spec prepare_user_ctx_params(name(), ctx()) -> ctx().
  prepare_user_ctx_params(HelperName = ?WEBDAV_HELPER_NAME, Params) ->
      Transformed = maps_flatmap(fun
          (Key = <<"onedataAccessToken">>, Token) when byte_size(Token) > 0 ->
              {ok, AdminId} = user_identity:get_or_fetch_user_id(Token),
              #{
  
negative.code: validate_user_ctx(#helper{name = StorageType}, UserCtx) ->
      validate_user_ctx(StorageType, UserCtx);
  
  
  validate_user_ctx(StorageType = ?WEBDAV_HELPER_NAME, UserCtx) ->
      FieldsBase = expected_user_ctx_params(StorageType),
      Fields = case UserCtx of
          #{<<"credentialsType">> := <<"none">>} ->
              FieldsBase;
          #{<<"credentialsType">> := _} ->
              % make "credentials" required rather than optional
              [<<"credentials">> | remove_field(<<"credentials">>, FieldsBase)];
          _ ->
              FieldsBase
      end,
      validate_fields(Fields, UserCtx);
  
  validate_user_ctx(StorageType, UserCtx) ->
      Fields = expected_user_ctx_params(StorageType),
      validate_fields(Fields, UserCtx).
  
  
  
  %%--------------------------------------------------------------------
  