Fixed - The drainToAsync method returns an incorrect value

Signed-off-by: seakider <seakider@gmail.com>

redisson/src/main/java/org/redisson/RedissonBoundedBlockingQueue.java

@@ -324,10 +324,6 @@ public class RedissonBoundedBlockingQueue<V> extends RedissonQueue<V> implements
     
     @Override
     public int drainTo(Collection<? super V> c, int maxElements) {
-        if (maxElements <= 0) {
-            return 0;
-        }
-
         return get(drainToAsync(c, maxElements));
     }
 
@@ -336,7 +332,10 @@ public class RedissonBoundedBlockingQueue<V> extends RedissonQueue<V> implements
         if (c == null) {
             throw new NullPointerException();
         }
-
+        if (maxElements <= 0) {
+            return new CompletableFutureWrapper<>(0);
+        }
+        
         return commandExecutor.evalWriteAsync(getRawName(), codec, new RedisCommand<Object>("EVAL", new ListDrainToDecoder(c)),
                 "local elemNum = math.min(ARGV[1], redis.call('llen', KEYS[1])) - 1;" +
                         "local vals = redis.call('lrange', KEYS[1], 0, elemNum); " +

redisson/src/test/java/org/redisson/RedissonBoundedBlockingQueueTest.java

@@ -621,6 +621,20 @@ public class RedissonBoundedBlockingQueueTest extends RedisDockerTest {
         assertThat(queue.remainingCapacity()).isEqualTo(100);
         Assertions.assertEquals(0, queue.size());
     }
+    
+    @Test
+    public void testDrainToAsync() throws ExecutionException, InterruptedException {
+        RBoundedBlockingQueue<Integer> queue = redisson.getBoundedBlockingQueue("queue");
+        queue.trySetCapacity(100);
+        for (int i = 0 ; i < 100; i++) {
+            assertThat(queue.offer(i)).isTrue();
+        }
+        Assertions.assertEquals(100, queue.size());
+        Set<Integer> batch = new HashSet<Integer>();
+        RFuture<Integer> future = queue.drainToAsync(batch, 0);
+        Assertions.assertEquals(future.get(), 0);
+        Assertions.assertEquals(batch.size(), 0);
+    }
 
     @Test
     public void testBlockingQueue() {