Those are just informational messages, that is why they say "INFO" not "ERROR"
Its just logging some system events like applicaiton start and end, and it logs tasks tha run, such as when you edit content there is a task that updates the search index.
Those nulls are just place holders for ip address, thread culture and url, not all events have a web request associated with them, only events that have a web request include that information so you see null on some events.
However if you see the application start and application end events happening frequently it can be a sign of a low memory environment because IIS will recycle the app whenever it reaches the limit of allocated memory.
Hope that helps,
Joe