Fix Lettuce exec to return null when pipelining

DATAREDIS-139

src/main/java/org/springframework/data/redis/connection/lettuce/LettuceConnection.java

@@ -460,7 +460,8 @@ public class LettuceConnection implements RedisConnection {
 		isMulti = false;
 		try {
 			if (isPipelined()) {
-				return Collections.singletonList((Object) asyncConn.exec());
+				 asyncConn.exec();
+				 return null;
 			}
 			return con.exec();
 		} catch (Exception ex) {

src/test/java/org/springframework/data/redis/connection/AbstractConnectionPipelineIntegrationTests.java

@@ -267,8 +267,7 @@ abstract public class AbstractConnectionPipelineIntegrationTests extends
 		assertNull(connection.get("key"));
 		assertNull(connection.exec());
 		List<Object> convertedResults = convertResults(connection.closePipeline());
-		assertEquals(Arrays.asList(new Object[] { Arrays.asList(new String[] { "OK", "value" }) }),
-				convertedResults);
+		assertEquals(Arrays.asList(new Object[] { "value" }), convertedResults);
 	}
 
 	@Test

src/test/java/org/springframework/data/redis/connection/lettuce/LettuceConnectionPipelineIntegrationTests.java

@@ -65,10 +65,6 @@ public class LettuceConnectionPipelineIntegrationTests extends
 	public void testUnwatch() throws Exception {
 	}
 
-	@Ignore("DATAREDIS-139 Lettuce exec while pipelining returns a non-null value")
-	public void testMultiExec() throws Exception {
-	}
-
 	@Ignore("DATAREDIS-140 Lettuce zCount/zInterStore methods execute synchronously when pipelining")
 	public void testZInterStoreAggWeights() {
 	}