* If subscription ID (most common) or other properties such as app ID are `nil`, the app crashes when requests for IAM impressions or clicks are created.
* The app will crash with Exception `[__NSPlaceholderDictionary initWithObjects:forKeys:count:]: attempt to insert nil object from objects[1]`
* Use a null-safe dictionary that will omit the entry if the value is null
* We choose to send these requests so we have record of 400-ing requests

* Add test module for In App Messages
* Add request tests for In App Messages including when some properties can be null
* And port over 2 existing IAM request tests