Hi,
siteSettings should not be null there and cannot be null there and work correctly. If it is null there then would need to figure out why that is happening and solve the underlying problem.
SiteSettings is cached so it does not have to be built on each request.
If the machine doesn't have enough memory or has a very slow connection to the db then it is likely to raise errors. db timeouts willl cause errors in any web app.
Joe