Linq-to-Sql Contains an int? inside a list of int
Another way to do this is to remove NULL values from the comparison to begin with, like so:

return Context.TblNumbers
              .Where(m =&gt; m.Number != null)
              .Where(m =&gt; convertedNumbers.Contains(m.Number.Value))
              .Select(m =&gt; m.Number.Value)
              .ToList();


I think this also reads more naturally since you only have the chance to match on non-null values anyway, instead of GetValueOrDefault() which implies you might need to get a default value.