This PR fixes a bug introduced by (@javiereguiluz) in #42165 (EDIT: No, I think it predates that now... #19623 @nicolas-grekas who replaced a bool with this code, which #42165 just refactored) ...

The code that was replaced was

if ($this->headerIsDumped !== (null !== $this->outputStream ? $this->outputStream : $this->lineDumper)) {

That was replaced in #42165 with code

if ($this->headerIsDumped !== ($this->outputStream ?? $this->lineDumper)) {

The correct code is proposed in this PR and is

if ($this->headerIsDumped !== (null !== ($this->outputStream ?? $this->lineDumper))) {

What is the bug/Why ?

So.... To replicate create a demo app with Symfony 5.4

composer create-project symfony/symfony-demo mySymfony54 1.8.0
cd mySymfony54
symfony serve
# Visit http://127.0.0.1:8000/en/blog/ to confirm its working
# Edit BlogController.php and throw an \Exception('test') in the index function
# Visit http://127.0.0.1:8000/en/blog/ to confirm you see the exception 
# Click the toolbar at the bottom to get to the Symfony Profiler
# Click LOGS in the left menu 
# Check console.log 

see console.log:

Click to open the error message and see overlapping text and no pretty-ness.

Once this PR is applied you then can repeat and you will see no console.log error message and you will see a pretty output like: