public List<Optional<? extends RequestManager>> entries() {
        return entries;
    }
{@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