Error assigning null to a nullable int - “The value 'null' is not valid for property”

Question

I have this property in my view model:

[DisplayName(\"Region\")]
public int? RegionId { get; set; }

I pass my view model to my controller,

Answer 1

I think the issue is not assigning null, it's that the consuming code does not except a null value. The assignment is perfectly valid (although your null check is inverted, and the cast is redundant).

viewModel.RegionId = null;

As an aside you can use HasValue to check for null on a nullable type. Although in reality this it's no different to a null check, just looks a bit cleaner:

if (viewModel.RegionId.HasValue)
{
    // do something
}