Object-Conventions-Best-Practices

Single Object 
Functions should return NULL object
Returning null is usually the best idea if you intend to indicate that no data is available.
http://stackoverflow.com/a/1626620/665387

List <Object>
Functions should return an EMPTY List<object>
It is considered a best practice to NEVER return null when returning a collection or enumerable. 
ALWAYS return an empty enumerable/collection.
http://stackoverflow.com/a/1970001/665387