This is often caused by an attempt to process a null object. An example, trying to empty a Bindable list that is null will trigger the exception:
public class MyViewModel {
[BindableProperty]
public virtual IList<Products> ProductsList{ get; set; }
public MyViewModel ()
{
ProductsList.Clear(); // here is the problem
}
}
This could easily be fixed by checking for null:
if (ProductsList!= null) ProductsList.Clear();