bug #44375 [DoctrineBridge] fix calling get_class on non-object (kbond)

This PR was merged into the 4.4 branch.

Discussion
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[DoctrineBridge] fix calling get_class on non-object

| Q             | A
| ------------- | ---
| Branch?       | 4.4
| Bug fix?      | yes
| New feature?  | no
| Deprecations? | no
| Tickets       | n/a
| License       | MIT
| Doc PR        | n/a

Discovered this bug while reviewing symfony/symfony#38662.

Commits
-------

70310ca9f3 [DoctrineBridge] fix calling get_class on non-object

Author: nicolas-grekas

Tests/Validator/Constraints/UniqueEntityValidatorTest.php

@@ -37,6 +37,7 @@
 use Symfony\Bridge\Doctrine\Validator\Constraints\UniqueEntity;
 use Symfony\Bridge\Doctrine\Validator\Constraints\UniqueEntityValidator;
 use Symfony\Component\Validator\Exception\ConstraintDefinitionException;
+use Symfony\Component\Validator\Exception\UnexpectedValueException;
 use Symfony\Component\Validator\Test\ConstraintValidatorTestCase;
 
 /**
@@ -821,6 +822,32 @@ public function testValidateUniquenessWithEmptyIterator($entity, $result)
         $this->assertNoViolation();
     }
 
+    public function testValueMustBeObject()
+    {
+        $constraint = new UniqueEntity([
+            'message' => 'myMessage',
+            'fields' => ['name'],
+            'em' => self::EM_NAME,
+        ]);
+
+        $this->expectException(UnexpectedValueException::class);
+
+        $this->validator->validate('foo', $constraint);
+    }
+
+    public function testValueCanBeNull()
+    {
+        $constraint = new UniqueEntity([
+            'message' => 'myMessage',
+            'fields' => ['name'],
+            'em' => self::EM_NAME,
+        ]);
+
+        $this->validator->validate(null, $constraint);
+
+        $this->assertNoViolation();
+    }
+
     public function resultWithEmptyIterator(): array
     {
         $entity = new SingleIntIdEntity(1, 'foo');

Validator/Constraints/UniqueEntityValidator.php

@@ -16,6 +16,7 @@
 use Symfony\Component\Validator\ConstraintValidator;
 use Symfony\Component\Validator\Exception\ConstraintDefinitionException;
 use Symfony\Component\Validator\Exception\UnexpectedTypeException;
+use Symfony\Component\Validator\Exception\UnexpectedValueException;
 
 /**
  * Unique Entity Validator checks if one or a set of fields contain unique values.
@@ -61,6 +62,10 @@ public function validate($entity, Constraint $constraint)
             return;
         }
 
+        if (!\is_object($entity)) {
+            throw new UnexpectedValueException($entity, 'object');
+        }
+
         if ($constraint->em) {
             $em = $this->registry->getManager($constraint->em);