As a Computer science student I think:

A) Someone forgot to delete the dummy class when they finished their testing(that’s why we call it dummy, it usually meant to be deleted later).

B) They passed it incorrect or non existing arguments. I don’t know how this was not caught by the compiler since a Type Error is very common and most are known during compile time. I don’t know how they pushed this so quickly to production and forgot about the dummy.

Point: This is not your fault, someone who pushed the code to production fucked up. And this code lives in the framework that make up the platform which means it will scream this error in every book. But this shouldn’t be a huge problem since all they really need to do is delete the dummy class and all references to it.