What does a JEDIS multi transaction exec returning null or empty request mean?

I am doing:

Transaction t = jedis.multi();
t.incr(key);
List<Object> response = t.exec();

This works well, but maybe 10 times a week the response is either null or it's an empty list. I read that this happens if the connection is closed, but no exception is being thrown. Is this null/empty response a "valid" response and what does it mean?