Returns the the non-null value of a simple nullable type.

Expression	Result
int? with the value null	0

The value of the current nullable object is returned if it has been assigned a valid underlying value otherwise 0 is returned.

Some expressions may require a non null value and yet your attribute is a nullable type. A scenario like this is catered for in MDriven OCL expressions.

.Value is available for all number types including Integer, Decimal, Double, Int64

For example

To calculate the Total Price of all products

Product.allinstances.Price->sum.Value

or

Product.allinstances->collect(i|i.Price.Value)->sum

This will ensure a value is always returned by the expression either when there are no product instances or product price is not set for all instances