[ci] fix create_database (#8498)
[ci] fix create_database (#8498)

If you look in the body of create_database, you will see that I copy the
keys from an existing sql-config using `get`. This propagates the `None`s
rather than leaving the keys missing. This fix changes `write_user_config`
to filter out keys set to None. Such keys should not appear in normal
configs because we never use `null` in our configs.
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