where i can find SystemCustomerAttributeNames in v4.6

i am trying to upgrade custom plugin from 4 to 4.6 so the old version is using service
need the SystemCustomerAttributeNames class

 var existingCouponCodes = EngineContext.Current.Resolve<IGenericAttributeService>().GetAttributeAsync<string>(SystemCustomerAttributeNames.DiscountCouponCode,
                genericAttributeService).GetAwaiter().GetResult();

so where i can find SystemCustomerAttributeNames in version 4.6? or it have alternative?
thanks in advance
hussainy

I think you are looking for this, https://github.com/nopSolutions/nopCommerce/blob/develop/src/Libraries/Nop.Core/Domain/Customers/NopCustomerDefaults.cs#L56

this code

 var firstName = customer.GetAttribute<string>(SystemCustomerAttributeNames.FirstName);

i am using it  in v 4.0.0
what is the equivalent of it in version 4.6
where i can find GetAttribute
and SystemCustomerAttributeNames.FirstName

Customer attributes moved to customer table
Check this out,
https://github.com/nopSolutions/nopCommerce/commit/8eb036aa69ecbaac64c73562af7a0e6f614bc792
Discussion: https://github.com/nopSolutions/nopCommerce/issues/4601