default PollResult pollOnClose() {
        return EMPTY;
    }
On shutdown of the {@link Consumer}, a request manager may need to send out network requests. Implementations
can signal that by returning the {@link PollResult close} requests here. Like {@link #poll(long)}, this method
is called within a single-threaded context from {@link ConsumerNetworkThread the consumer's network I/O thread}.
As such, there should be no need for synchronization protection in this method's implementation.

<p/>

<em>Note</em>: no network I/O occurs in this method. The method itself should not block for any reason. This
method is called as an (indirect) result of {@link Consumer#close() the consumer's close method} being invoked.
(Note that it is still invoked on the consumer's network I/O thread). Quick execution of this method in
<em>all</em> request managers is critical to ensure that we can complete as many of the consumer's shutdown
tasks as possible within the user-provided timeout.
clients/src/main/java/org/apache/kafka/clients/consumer/internals/RequestManager.java