From b7011ebe5df19cf26b71cbcc39250b4094262116 Mon Sep 17 00:00:00 2001
From: Lucio Paiva <luciopaiva@gmail.com>
Date: Wed, 12 Jul 2023 18:56:01 +0100
Subject: [PATCH] Fix NPE when manually flushing a batch

When manually flushing a batch with a set size, we could potentially run into a NPE if the command queue is empty when flush() is called.
---
 .../io/lettuce/core/dynamic/SimpleBatcher.java   |  8 ++++----
 .../RedisCommandsBatchingIntegrationTests.java   | 16 ++++++++++++++++
 2 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/src/main/java/io/lettuce/core/dynamic/SimpleBatcher.java b/src/main/java/io/lettuce/core/dynamic/SimpleBatcher.java
index 3f2edf951b..e131d8db4c 100644
--- a/src/main/java/io/lettuce/core/dynamic/SimpleBatcher.java
+++ b/src/main/java/io/lettuce/core/dynamic/SimpleBatcher.java
@@ -35,6 +35,7 @@
  * </ul>
  *
  * @author Mark Paluch
+ * @author Lucio Paiva
  */
 class SimpleBatcher implements Batcher {
 
@@ -148,12 +149,12 @@ private List<RedisCommand<Object, Object, Object>> prepareForceFlush() {
 
         List<RedisCommand<Object, Object, Object>> batch = new ArrayList<>(Math.max(batchSize, 10));
 
-        do {
+        while (!queue.isEmpty()) {
+
             RedisCommand<Object, Object, Object> poll = queue.poll();
 
-            assert poll != null;
             batch.add(poll);
-        } while (!queue.isEmpty());
+        }
 
         return batch;
     }
@@ -166,7 +167,6 @@ private List<RedisCommand<Object, Object, Object>> prepareDefaultFlush(int consu
 
             RedisCommand<Object, Object, Object> poll = queue.poll();
 
-            assert poll != null;
             batch.add(poll);
         }
 
diff --git a/src/test/java/io/lettuce/core/dynamic/RedisCommandsBatchingIntegrationTests.java b/src/test/java/io/lettuce/core/dynamic/RedisCommandsBatchingIntegrationTests.java
index ea9e60c299..adbfa5cac3 100644
--- a/src/test/java/io/lettuce/core/dynamic/RedisCommandsBatchingIntegrationTests.java
+++ b/src/test/java/io/lettuce/core/dynamic/RedisCommandsBatchingIntegrationTests.java
@@ -42,6 +42,7 @@
 
 /**
  * @author Mark Paluch
+ * @author Lucio Paiva
  */
 @ExtendWith(LettuceExtension.class)
 class RedisCommandsBatchingIntegrationTests extends TestSupport {
@@ -99,6 +100,16 @@ void selectiveBatchingShouldHandleErrors() {
         }
     }
 
+    @Test
+    void shouldNotCrashWhenFlushCalledWithEmptyQueue() {
+
+        RedisCommandFactory factory = new RedisCommandFactory(redis.getStatefulConnection());
+
+        SelectiveBatchingWithSize api = factory.getCommands(SelectiveBatchingWithSize.class);
+
+        api.flush();
+    }
+
     @Test
     void shouldExecuteBatchingSynchronously() {
 
@@ -215,4 +226,9 @@ static interface SelectiveBatching extends Commands, BatchExecutor {
 
     }
 
+    @BatchSize(5)
+    interface SelectiveBatchingWithSize extends Commands, BatchExecutor {
+
+    }
+
 }