Extension methods not taken into account during analysis

Hi,

Is there a way to configure ReSharper to take into account my extension methods while analyzing the code?

I created this extension method:

public static bool IsNullOrEmpty<T>( this List<T> source )
{
    return source == null || source.Count == 0;
}

When I use it (see below), I get a warning (Possible NullReferenceException) that is irrelevant.

public void DoSomething(IEnumerable<int> collection)
{
    var list = collection?.ToList();

    if (!list.IsNullOrEmpty())
    {
        foreach (var item in list) // warning here
        {
            // Do something
        }
    }
}

I'm using ReSharper 10.0.2

Thanks!