fix handling empty data in ValueToDuplicatesTransformer

The transformer receives the data of child forms that have already been
through the transformation schema. If no custom view transformer was used
on that child form the empty would already have been changed to null.
Thus, receiving an empty string here means that the child form explicitly
asked for it and the value must not be exchanged with null.

Author: xabbuh

Extension/Core/DataTransformer/ValueToDuplicatesTransformer.php

@@ -62,7 +62,7 @@ public function reverseTransform($array)
         $emptyKeys = [];
 
         foreach ($this->keys as $key) {
-            if (isset($array[$key]) && '' !== $array[$key] && false !== $array[$key] && [] !== $array[$key]) {
+            if (isset($array[$key]) && false !== $array[$key] && [] !== $array[$key]) {
                 if ($array[$key] !== $result) {
                     throw new TransformationFailedException('All values in the array should be the same.');
                 }

Tests/Extension/Core/DataTransformer/ValueToDuplicatesTransformerTest.php

@@ -70,7 +70,7 @@ public function testReverseTransformCompletelyEmpty()
             'c' => '',
         ];
 
-        $this->assertNull($this->transformer->reverseTransform($input));
+        $this->assertSame('', $this->transformer->reverseTransform($input));
     }
 
     public function testReverseTransformCompletelyNull()

Tests/Extension/Core/Type/RepeatedTypeTest.php

@@ -11,6 +11,7 @@
 
 namespace Symfony\Component\Form\Tests\Extension\Core\Type;
 
+use Symfony\Component\Form\Extension\Core\Type\TextType;
 use Symfony\Component\Form\Form;
 use Symfony\Component\Form\Tests\Fixtures\NotMappedType;
 use Symfony\Component\OptionsResolver\Exception\InvalidOptionsException;
@@ -191,6 +192,36 @@ public function testSetOptionsPerChildAndOverwrite()
         $this->assertTrue($form['second']->isRequired());
     }
 
+    /**
+     * @dataProvider emptyDataProvider
+     */
+    public function testSubmitNullForTextTypeWithEmptyDataOptionSetToEmptyString($emptyData, $submittedData, $expected)
+    {
+        $form = $this->factory->create(static::TESTED_TYPE, null, [
+            'type' => TextType::class,
+            'options' => [
+                'empty_data' => $emptyData,
+            ]
+        ]);
+        $form->submit($submittedData);
+
+        $this->assertSame($expected, $form->getData());
+    }
+
+    public static function emptyDataProvider()
+    {
+        yield ['', null, ''];
+        yield ['', ['first' => null, 'second' => null], ''];
+        yield ['', ['first' => '', 'second' => null], ''];
+        yield ['', ['first' => null, 'second' => ''], ''];
+        yield ['', ['first' => '', 'second' => ''], ''];
+        yield [null, null, null];
+        yield [null, ['first' => null, 'second' => null], null];
+        yield [null, ['first' => '', 'second' => null], null];
+        yield [null, ['first' => null, 'second' => ''], null];
+        yield [null, ['first' => '', 'second' => ''], null];
+    }
+
     public function testSubmitUnequal()
     {
         $input = ['first' => 'foo', 'second' => 'bar'];