DATAREDIS-289 - Avoid NPE in DefaultValueOperations#append() in case of pipelining or/and multi/exec calls.

We now return null if DefaultValueOperations#append() was applied to a non-existing list and thus returned null. Previously a NPE was thrown in case of pipelining or/and multi/exec calls.

Original pull request: #48.

src/main/java/org/springframework/data/redis/core/DefaultValueOperations.java

@@ -84,7 +84,8 @@ class DefaultValueOperations<K, V> extends AbstractOperations<K, V> implements V
 		return execute(new RedisCallback<Integer>() {
 
 			public Integer doInRedis(RedisConnection connection) {
-				return connection.append(rawKey, rawString).intValue();
+				final Long result = connection.append(rawKey, rawString); 				
+				return ( result != null ) ? result.intValue() : null; 
 			}
 		}, true);
 	}