Use Apex-Defined Data Type Collection Variables with Operators in Assignment and Decision Elements
Where: This change applies to Lightning Experience and Salesforce Classic in Enterprise, Performance, Unlimited, and Developer editions.
Why: For example, a flow uses an Apex-defined collection variable to store a list of car registrations from a system outside of Salesforce. Now you can use a Decision element to check whether a car registration already exists in the list of registrations from the external system.
If the registration isn’t already in the list of registrations, you can add it to the list using an Assignment element.