Anyone know how I can set a default value for an average? I have a line like this...

```
dbPlugins = (from p in dbPlugins
                select new { Plugin = p, AvgScore = p.DbVersions.Average(x => x.DbRatings.Average(y => y.Score)) })
            .OrderByDescending(x => x.AvgScore)
            .Select(x => x.Plugin).ToList();

```

which throws an error becase I have no ratings yet. If I have none I want the average to default to 0. I was thinking this should be an extension method where I could specify what the default value should be.