minor #6343 Remove an unneeded comparison in FileUploadType (javiereg…

…uiluz)

This PR was merged into the 4.x branch.

Discussion
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Remove an unneeded comparison in FileUploadType

This fixes:

```
Error: Strict comparison using !== between '' and non-falsy-string will always evaluate to true.
 ------ ------------------------------------------------------------------
  Line   Form/Type/FileUploadType.php
 ------ ------------------------------------------------------------------
  [15](https://github.com/EasyCorp/EasyAdminBundle/actions/runs/9535095150/job/26280406642?pr=6328#step:5:16)1    Strict comparison using !== between '' and non-falsy-string will
         always evaluate to true.
 ------ ------------------------------------------------------------------
```

Commits
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ea71c30 Remove an unneeded comparison in FileUploadType

src/Form/Type/FileUploadType.php

@@ -148,7 +148,7 @@ public function configureOptions(OptionsResolver $resolver): void
                 $value = $this->projectDir.'/'.$value;
             }
 
-            if (!$isStreamWrapper && '' !== $value && (!is_dir($value) || !is_writable($value))) {
+            if (!$isStreamWrapper && (!is_dir($value) || !is_writable($value))) {
                 throw new InvalidArgumentException(sprintf('Invalid upload directory "%s" it does not exist or is not writable.', $value));
             }