We have seen a panic when re-joining a node to a swarm cluster. The
cause of the issue is unknown, so we just need to add a test for nil
objects and log when we get the condition. Hopefully this can prevent
the crash and we can recover the config at a later time.
Signed-off-by: Stephen J Day <stephen.day@docker.com>
Upstream-commit: 454128c6e82cded211c1412e3eb350b1f7533ee2
Component: engine
95a3a5cb78