bug #57815 [Console][PhpUnitBridge][VarDumper] Fix NO_COLOR empty value handling (alexandre-daubois)

This PR was merged into the 5.4 branch.

Discussion
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[Console][PhpUnitBridge][VarDumper] Fix `NO_COLOR` empty value handling

| Q             | A
| ------------- | ---
| Branch?       | 5.4
| Bug fix?      | yes
| New feature?  | no
| Deprecations? | no
| Issues        | symfony/symfony#57777 (comment)
| License       | MIT

`NO_COLOR` must be non-empty in order to be considered enabled (https://no-color.org/):

> when present and not an empty string (regardless of its value)

Commits
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6a96ff9116 [Console][PhpUnitBridge][VarDumper] Fix `NO_COLOR` empty value handling

Author: nicolas-grekas

Dumper/CliDumper.php

@@ -606,7 +606,7 @@ private function hasColorSupport($stream): bool
         }
 
         // Follow https://no-color.org/
-        if (isset($_SERVER['NO_COLOR']) || false !== getenv('NO_COLOR')) {
+        if ('' !== ($_SERVER['NO_COLOR'] ?? getenv('NO_COLOR') ?: '')) {
             return false;
         }