Symfony version(s) affected: 2.8+

Description
I have found that setNotModified() method empties the content, but StreamedResponse class uses a callback for the output, so when the response returns a 304 code, it will output the content too, when it shouldn't.

Possible Solution
I think the method setNotModified() should be overriden by StreamedResponse class, and there set an empty closure as callback.