Github user patricker commented on the issue:
https://github.com/apache/nifi/pull/2629
The database error only propagates if `isClosed` returns false; I was
thinking that it might be possible to have a connection close before all
results are read. The documentation isn't clear on this point, it just says
isClosed will be true either when specifically closed, or if automatically
closed... which basically leaves it open to any circumstance a driver might
want to cover...---
