minor #32561 [Config][ReflectionClassResource] Use ternary instead of null coalescing operator (fancyweb)

This PR was merged into the 3.4 branch.

Discussion
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[Config][ReflectionClassResource] Use ternary instead of null coalescing operator

| Q             | A
| ------------- | ---
| Branch?       | 3.4
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

`??` cannot be on 3.4, tests are failing because of this.

Commits
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4db953f40c [Config][ReflectionClassResource] Use ternary instead of null coaelscing operator

src/Symfony/Component/Config/Resource/ReflectionClassResource.php

@@ -140,7 +140,7 @@ class ReflectionClassResource implements SelfCheckingResourceInterface, \Seriali
 
             foreach ($class->getProperties(\ReflectionProperty::IS_PUBLIC | \ReflectionProperty::IS_PROTECTED) as $p) {
                 yield $p->getDocComment().$p;
-                yield print_r($defaults[$p->name] ?? null, true);
+                yield print_r(isset($defaults[$p->name]) ? $defaults[$p->name] : null, true);
             }
         }