"ERROR parsing time" message

When doing a dry run (without execute), the following error is in the output:

```
2018/09/12 18:36:16 binlogsyncer.go:573: [info] rotate to (mysql-bin-changelog.039985, 41113243)
2018-09-12 18:36:16 ERROR parsing time "" as "2006-01-02T15:04:05.999999999Z07:00": cannot parse "" as "2006"
# Migrating `...`.`...`; Ghost table is `...`.`...`
```

The command is run with options:

```
--user="root"
--password="..." --port=3306
--host="ghost-db...."
--database="..."
--table="..."
--alter="ADD INDEX \`...\` (\`site\`, \`item_id\`, \`day\`) "
--assume-rbr
--hooks-path="/opt/ghost/hooks"
--panic-flag-file=/opt/ghost/flags/ghost.panic.flag
```

As far as I can tell, nothing actually goes wrong and the process succeeds, but it's an ERROR in capital letters anyway :)
It has been spotted before: https://github.com/github/gh-ost/issues/505#issuecomment-338548363 but it doesn't look like there was any followup.

I'm running version 1.0.46.
The database is AWS Aurora 5.6.