public SELF onServerErrorStatus() {
        return onStatusClass(HttpStatusClass.SERVER_ERROR);
    }
Adds the {@link HttpStatusClass#SERVER_ERROR}.

<p>When this is used for a {@link CircuitBreakerRule}, and the response status is
{@link HttpStatusClass#SERVER_ERROR}, a {@link Response} is reported as a success or failure to a
{@link CircuitBreaker} or ignored depending on the build methods({@code #thenSuccess()},
{@code #thenFailure()} and {@code #thenIgnore()}).
core/src/main/java/com/linecorp/armeria/client/AbstractRuleBuilder.java