change report for notToEqualNull

[robstoll]

Platform (jvm, js, android): Extension (none, kotlin 1.3, jdk8): none

Code related feature

expect(null as List<Int>?).notToEqualNull {
  toBeEmpty()
}

For this we currently see in reporting

expect: null
◆ is instance of type: List (kotlin.collections.List) -- Class: java.util.List
  » is: empty

And we would like to see the following instead

expect: null
◆ is not: null but is instance of: List (kotlin.collections.List) -- Class: (java.util.List)
  » is: empty

This means notToEqualNull has to do more than just delegating to toBeAnInstanceOf hence:

• don't delegate simply to isA in DefaultAnyAssertions.notToBeNullBut
• copy implementation of isA but change the options, to be more precise, change the description and the representation
• change the implementation of notToBe treat null specially so that expect(null as List<Int>?).notToBe(null) also results in the reporting above (without is: empty of course)

---

Please react with :+1: if you would like to see this feature implemented in Atrium, the more upvotes the more likely I will implement it myself -- feel free to sponsor me, that would be a motivation too. You are of course welcome to work on this issue. Write I'll work on it as comment so that we can assign the task to you.