Fix updates of NULL appconfig values
Fix updates of NULL appconfig values

The comparisson of NULL is a bit special.
So we need to handle this a tad beter else it might not replace NULL
values. or allow you to set NULL values on updates.

Signed-off-by: Roeland Jago Douma <982d370f7dc34a05b4abe8788f899578d515262d@famdouma.nl>

nextcloud/server,nextcloud/server,andreas-p/nextcloud-server,andreas-p/nextcloud-server,andreas-p/nextcloud-server,nextcloud/server,andreas-p/nextcloud-server,nextcloud/server,andreas-p/nextcloud-server