mqtt5_clinet master have a error about :_TypeError (type '(MqttMessage) => bool' is not a subtype of type '((MqttMessage?) => bool)?' of 'callback') #11
the migration to null safety is not yet complete, you should not be using the master branch of the repo, only published package versions. see my comments on #8
return await super.connect(username, password);
Exception has occurred. _TypeError (type '(MqttMessage) => bool' is not a subtype of type '((MqttMessage?) => bool)?' of 'callback')