I am developing a automatic record replay system for testing.How can i access EventSystem from one Monobehaviour class to another class

I am implementing a record replay system.For this i am having a class which should be capable of accessing the application under test. I need to access the EventSystem of the application under test. I am trying to pass it as a function parameter.I have a function which can accept a EventSystem.But i am getting error as System.nullReferenceException:Object reference not set to instance of an object.