public Set<Long> filteredProducerIds() {
        return filteredProducerIds;
    }
Returns the set of producerIds that are being filtered or empty if none have been specified.

@return the current set of filtered states (empty means that no producerIds are filtered and
        all transactions will be returned)
clients/src/main/java/org/apache/kafka/clients/admin/ListTransactionsOptions.java