The replSetReconfig command does a no-op write, but does not check that the node is still primary before doing so. Since the command only takes a lock when writing down the config document, it is possible for the primary to stepdown and transition to secondary before doing this no-op write.

We end up calling onInternalOpMessage, which will pass in an empty namespace. Because of this, we don't actually do the primary check in _logOpsInner. This would mean that we can allow the reconfig no-op write to occur on a secondary.

This is tracked separately from SERVER-47142 since we would like to backport this change to 4.2 and earlier affected versions.