Spock mocking abstract class throws InvocationTargetException

I'm using spring boot MVC and want to test my service class using spock. I'm running into an issue however with instantiating a mock object however, and get the following error:

public static Object invokeMethod(Object target, Method method, Object... args) {
        try {
            return method.invoke(target, args);
        } catch (IllegalAccessException var4) {
            ExceptionUtil.sneakyThrow(var4);
            return null;
        } catch (InvocationTargetException var5) {
            **ExceptionUtil.sneakyThrow(var5.getCause());**
            return null;
        }
    }

With the line that has the ** being the cause of my issue. I'm not sure why this is occurring however. Below is what I'm doing.

@Autowired
MyService myService

def "deleting"(){
    given "creating a basic object with uuid"
    ObjectDefinition object = Mock()
    myService.saveNewObject(object)
}

Where ObjectDefinition is an abstract class, and inside of the MyService class I have a data access object to talk to the database as well. Why do I keep getting the following error when I try running this piece of code, and what do I need to do to fix it?