NullPinterException flushing the buffer.

[jdelgadoalfonso]

https://github.com/galgus/kafka-connect-redis/blob/develop/src/main/java/net/galgus/kafka/connect/redis/source/RedisBacklogEventBuffer.java#L128

java.lang.NullPointerException: Cannot invoke "java.io.ObjectOutputStream.flush()" because "this.objectOutputStream" is null
        at net.galgus.kafka.connect.redis.source.RedisBacklogEventBuffer.getAvailableEvents(RedisBacklogEventBuffer.java:128)
        at net.galgus.kafka.connect.redis.source.RedisSourceTask.poll(RedisSourceTask.java:166)
        at org.apache.kafka.connect.runtime.AbstractWorkerSourceTask.poll(AbstractWorkerSourceTask.java:452)
        at org.apache.kafka.connect.runtime.AbstractWorkerSourceTask.execute(AbstractWorkerSourceTask.java:346)
        at org.apache.kafka.connect.runtime.WorkerTask.doRun(WorkerTask.java:189)
        at org.apache.kafka.connect.runtime.WorkerTask.run(WorkerTask.java:244)
        at org.apache.kafka.connect.runtime.AbstractWorkerSourceTask.run(AbstractWorkerSourceTask.java:72)
        at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:539)
        at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
        at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136)
        at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
        at java.base/java.lang.Thread.run(Thread.java:833)