Ignore subscriptions without topic defined

[adrymyry]

:tophat: What?

Ignore subscriptions that do not define a topic name.

:thinking: Why?

Autodiscovery support for class-based Subscriptions (https://github.com/mercadona/rele/issues/161) opens the possibility to create generic classes with shared behavior between subclasses.

class GenericClass(Subscription):
    topic = None

    def __init__(self):
        self._func = self.callback_func
        super().__init__(self._func, self.topic)

    def callback_func(self, data, **kwargs):
        return data["type"]

class ClassA(GenericClass):
    topic = "topic-for-A-messages"
    
class ClassB(GenericClass):
    topic = "topic-for-B-messages"

GenericClass is a subclass of Subscription so it will be loaded in the autodiscovery process. However, it does not seem reasonable since it will not be subscribed to any topic.

[antoniobusrod]

What do you think to raise a warning instead of skipping these subscriptions? I think we should be explicit and generic about the content which should be exist in the subs modules.

[jonasae]

PR discontinued.