mqtt5_clinet master have a error about :_TypeError (type '(MqttMessage) => bool' is not a subtype of type '((MqttMessage?) => bool)?' of 'callback')

[tongweizj]

return await super.connect(username, password);

Exception has occurred.
_TypeError (type '(MqttMessage) => bool' is not a subtype of type '((MqttMessage?) => bool)?' of 'callback')

[shamblett]

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