empty collection error / collection range error
Currently, if you try to get item 0 from a collection, and the collection is empty, the workflow TERMINATES. Ideally, the workflow would error, and there would be a way to try / catch the error, but there isn't. Your workflow just stops running, and there is no email or any other kind of indication that there is a problem with your workflow. How do you manage this without throwing an error? There is no way to test the number of items in the collection to avoid this TERMINATION.
Before I get item 0 I use the Count Items in Collection action. Then a conditional branch to check if the count variable is greater than zero. If it is, grab item 0.
Nintex Support Case #00392163 - Workflow termination on empty collection - As per the dev team it is by design so we cannot escalate it.