public void Can_clear_key()
{
var entityType = new EntityType(typeof(Customer));
var property1 = entityType.AddProperty(Customer.IdProperty);
var property2 = entityType.AddProperty(Customer.NameProperty);
entityType.SetKey(property1, property2);
Assert.Equal(2, entityType.GetKey().Properties.Count());
entityType.SetKey(null);
Assert.Null(entityType.TryGetKey());
}