access log doesn't support %{r,xxx}

AccessLogHandler's javadoc mentions:

%{r,xxx} xxx is an attribute in the ServletRequest

But adding the following to access log pattern

%{r,javax.servlet.error.status_code}

results in a server log message:

19:55:55,432 ERROR [undertow] (MSC service thread 1-6) UT005017: Unknown variable %{r,javax.servlet.error.status_code}