How should the specification pattern handle null candidates?

Question

I am just wondering if there is a recommended strategy for dealing with null candidates in the specification pattern. As I see it, there are two possible strategies:

Throw an exception if the candidate is null.
Return false for cases where null is not a valid candidate value.

Examples are written in Kotlin, but this could easily apply to C# and Java as well.

Example - Throw an exception

class RangeSpecification<T : Comparable<T>>(
    private val min: T,
    private val max: T
) : Specification<T?>() {

    override fun isSatisfiedBy(candidate: T?): Boolean {
        checkNotNull(candidate) 
        // ^ Throws IllegalStateException("Required value was null.")
        return candidate in min..max
    }
}

Example - Return false

class RangeSpecification<T : Comparable<T>>(
    private val min: T,
    private val max: T
) : Specification<T?>() {

    override fun isSatisfiedBy(candidate: T?): Boolean {
        return candidate != null && candidate in min..max
    }
}

I'm not sure whether this qualifies as an opinionated question (and apologies if that's the case), but I'm just wondering which approach is more suitable in line with the specification pattern?

References

I think it depends entirely on the domain and whether `null` is a valid value for `candidate` or represents an error condition. — jaco0646, Jan 17 '19 at 04:15

How should the specification pattern handle null candidates?

0 Answers0