public static <U> EventLoopCheckingFuture<U> completedFuture(@Nullable U value) {
        final EventLoopCheckingFuture<U> future = new EventLoopCheckingFuture<>();
        future.complete(value);
        return future;
    }
Returns an {@link EventLoopCheckingFuture} which has been completed with the specified {@code value}.
core/src/main/java/com/linecorp/armeria/common/util/EventLoopCheckingFuture.java