void addAll(Collection<CompletedFetch> completedFetches) {
        if (completedFetches == null || completedFetches.isEmpty())
            return;

        try {
            lock.lock();
            this.completedFetches.addAll(completedFetches);
            notEmptyCondition.signalAll();
        } finally {
            lock.unlock();
        }
    }
Return whether we have any completed fetches pending return to the user. This method is thread-safe. Has
visibility for testing.

@return {@code true} if there are completed fetches that match the {@link Predicate}, {@code false} otherwise
clients/src/main/java/org/apache/kafka/clients/consumer/internals/FetchBuffer.java