Nullables "Possible 'System.InvalidOperationException'"

I can't quite get what ReSharper is complaining about? Is is access to modified closures (nah?)...

public class Foo
{
   public int? FooValue;
}

public void DoBar(Foo foo)
{
   var e = Enumerable.Empty<int>();


   if(foo != null && foo.FooValue.HasValue)
   {
      var values = e.First(i => i == foo.FooValue.Value); // foo.FooValue.Value is causing this
   }
}