public void ClearWithoutNull()
{
var lookup = new MutableLookup<string, string>();
lookup.Add("F", "Foo");
lookup.Add("F", "Foobar");
lookup.Add("B", "Bar");
lookup.Clear();
Assert.AreEqual (0, lookup.Count);
Assert.IsFalse (lookup.Contains ("F"));
Assert.IsFalse (lookup.Contains ("B"));
}