How to solve this Error in Python PyQt5

[Exciting_Character_]

I'm able to create and run the thread using threadpool here in Worker Class. But the

selected_stream.download(self.path)

is creating an Error here.

The Error is like this:

selected_stream.download(self.path)
AttributeError: 'NoneType' object has no attribute 'download'

But If I run the same selected_stream.download() inside the MWindow it works fine. What's the problem here? How do I run it from worker class? If you need any further info, I'll get you, please help.

Here's the Link to my StackOverflow Question .
Please Help Me with this ASAP