I was doing some Linq programming and kept hitting the problem where if there were no results to a query, but I wanted to call First() or Single() to get a single row, I kept getting “Sequence contains no elements” exceptions.
There didn’t seem to be an easy way to tell if the resultset was null, because it wasn’t really NULL, not in a C# sense. And trying to get Count() would throw a separate exception if there really was at least one element, because I couldn’t enumerate a sequence more than once.
Luckily an offhand comment by Scott Guthrie on his blog helped me out a lot. Use FirstOrDefault() with a dummy criteria as an argument:
var record = <blah>.GetResult().FirstOrDefault(p => p.id <0)
If there are no results, this code will return NULL to the variable, which you can then easily check in your code.