[x] All of your commits have been signed-off with the correct email address (The same one that you used to sign the CLA)
[x] If This PR fixes an issue, that you reference the issue below. OR if this is a new issue that you are fixing straight away that you add some Description about the bug and how this will fix it.
[x] If this is new functionality, You have added the appropriate Unit tests.
Always returning null breaks the contract set in the function signature and documentation.
This affects all subscribes that receive
IMqttMessageListener
as parameter.Please make sure that the following boxes are checked before submitting your Pull Request, thank you!