minor #59898 replace assertEmpty() with stricter assertions (xabbuh)

This PR was merged into the 7.3 branch.

Discussion
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replace `assertEmpty()` with stricter assertions

| Q             | A
| ------------- | ---
| Branch?       | 7.3
| Bug fix?      | no
| New feature?  | no
| Deprecations? | no
| Issues        |
| License       | MIT

In the code we are strict about not using `empty()`. In my opinion it makes sense to be equally strict with our assertions. But I'd like to gather some feedback first before updating all places.

Commits
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6550cb815e3 replace assertEmpty() with stricter assertions

Author: fabpot

Tests/Validator/DoctrineLoaderTest.php

@@ -210,7 +210,7 @@ public function testClassNoAutoMapping()
         $this->assertSame(AutoMappingStrategy::DISABLED, $classMetadata->getAutoMappingStrategy());
 
         $maxLengthMetadata = $classMetadata->getPropertyMetadata('maxLength');
-        $this->assertEmpty($maxLengthMetadata);
+        $this->assertSame([], $maxLengthMetadata);
 
         /** @var PropertyMetadata[] $autoMappingExplicitlyEnabledMetadata */
         $autoMappingExplicitlyEnabledMetadata = $classMetadata->getPropertyMetadata('autoMappingExplicitlyEnabled');