Fixed Exec return type for cluster client. Now returns Array or Null. (…

…#1019)

* Fixed Exec return type for cluster client. Now returns Array or Null.

* Added test for when watch transaction failure returns null.

java/client/src/main/java/glide/api/RedisClusterClient.java

@@ -71,14 +71,14 @@ protected ClusterValue<Object> handleCustomCommandResponse(Route route, Response
     @Override
     public CompletableFuture<Object[]> exec(ClusterTransaction transaction) {
         return commandManager.submitNewCommand(
-                transaction, Optional.empty(), this::handleArrayResponse);
+                transaction, Optional.empty(), this::handleArrayOrNullResponse);
     }
 
     @Override
     public CompletableFuture<ClusterValue<Object>[]> exec(
             ClusterTransaction transaction, Route route) {
         return commandManager
-                .submitNewCommand(transaction, Optional.ofNullable(route), this::handleArrayResponse)
+                .submitNewCommand(transaction, Optional.ofNullable(route), this::handleArrayOrNullResponse)
                 .thenApply(
                         objects ->
                                 Arrays.stream(objects)

java/integTest/src/test/java/glide/cluster/ClusterTransactionTests.java

@@ -3,8 +3,11 @@
 
 import static glide.TransactionTestUtilities.transactionTest;
 import static glide.TransactionTestUtilities.transactionTestResult;
+import static glide.api.BaseClient.OK;
 import static glide.api.models.configuration.RequestRoutingConfiguration.SimpleRoute.RANDOM;
 import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNull;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import glide.TestConfiguration;
@@ -50,6 +53,17 @@ public void custom_command_info() {
         assertTrue(((String) result[0]).contains("# Stats"));
     }
 
+    @Test
+    @SneakyThrows
+    public void WATCH_transaction_failure_returns_null() {
+        ClusterTransaction transaction = new ClusterTransaction();
+        transaction.get("key");
+        assertEquals(
+                OK, clusterClient.customCommand(new String[] {"WATCH", "key"}).get().getSingleValue());
+        assertEquals(OK, clusterClient.set("key", "foo").get());
+        assertNull(clusterClient.exec(transaction).get());
+    }
+
     @Test
     @SneakyThrows
     public void info_simple_route_test() {