@Override
    public void close() {
        closer.close(
                () -> {
                    log.debug("Closing RequestManagers");

                    entries.stream()
                            .filter(Optional::isPresent)
                            .map(Optional::get)
                            .filter(rm -> rm instanceof Closeable)
                            .map(rm -> (Closeable) rm)
                            .forEach(c -> closeQuietly(c, c.getClass().getSimpleName()));
                    log.debug("RequestManagers has been closed");
                },
                () -> log.debug("RequestManagers was already closed")
        );
    }
{@code RequestManagers} provides a means to pass around the set of {@link RequestManager} instances in the system.
This allows callers to both use the specific {@link RequestManager} instance, or to iterate over the list via
the {@link #entries()} method.
clients/src/main/java/org/apache/kafka/clients/consumer/internals/RequestManagers.java