goja-core/src/main/java/goja/core/kits/reflect/ClassKit.java
public static Class<?> getUserClass(Object instance) {
        Preconditions.checkNotNull(instance, "Instance must not be null");
        return getUserClass(instance.getClass());
    }
public static Class<?> getUserClass(Object instance) {
        Preconditions.checkNotNull(instance, "Instance must not be null");
        return getUserClass(instance.getClass());
    }
Return the user-defined class for the given instance: usually simply
the class of the given instance, but the original class in case of a
CGLIB-generated subclass.

@param instance the instance to check
@return the user-defined class