@Nullable
    default Boolean reportBlockedEventLoop() {
        return null;
    }
Returns whether {@link CompletableFuture}s returned by Armeria methods log a warning if
{@link CompletableFuture#join()} or {@link CompletableFuture#get()} are called from an event loop thread.
Blocking an event loop thread in this manner reduces performance significantly, possibly causing
deadlocks, so it should be avoided at all costs (e.g. using {@code thenApply()} type methods to execute
asynchronously or running the logic using {@link ServiceRequestContext#blockingTaskExecutor()}.

<p>This flag is enabled by default.
Specify the {@code -Dcom.linecorp.armeria.reportBlockedEventLoop=false} JVM option
to disable it.
core/src/main/java/com/linecorp/armeria/common/FlagsProvider.java