minor symfony#20425 [Form] fixed "empty_value" option deprecation (HeahDude)

This PR was merged into the 2.7 branch.

Discussion
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[Form] fixed "empty_value" option deprecation

| Q             | A
| ------------- | ---
| Branch?       | 2.x only
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | symfony#15945 (comment)
| License       | MIT
| Doc PR        | ~

I didn't make any profiling but a resolver instance is passed to `configureOptions()` creating locale variables including those exceptions for each field using one of the patched form types, so I guess the memory usage can grow really fast.

Commits
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7e84907 [Form] fixed "empty_value" option deprecation

Author: fabpot

src/Symfony/Component/Form/Extension/Core/Type/ChoiceType.php

@@ -39,6 +39,11 @@
 
 class ChoiceType extends AbstractType
 {
+    /**
+     * @internal To be removed in 3.0
+     */
+    const DEPRECATED_EMPTY_VALUE = '__deprecated_empty_value__';
+
     /**
      * Caches created choice lists.
      *
@@ -336,7 +341,7 @@ public function configureOptions(OptionsResolver $resolver)
         };
 
         $placeholderNormalizer = function (Options $options, $placeholder) use ($that) {
-            if (!is_object($options['empty_value']) || !$options['empty_value'] instanceof \Exception) {
+            if ($that::DEPRECATED_EMPTY_VALUE !== $options['empty_value']) {
                 @trigger_error(sprintf('The form option "empty_value" of the "%s" form type (%s) is deprecated since version 2.6 and will be removed in 3.0. Use "placeholder" instead.', $that->getName(), __CLASS__), E_USER_DEPRECATED);
 
                 if (null === $placeholder || '' === $placeholder) {
@@ -388,7 +393,7 @@ public function configureOptions(OptionsResolver $resolver)
             'preferred_choices' => array(),
             'group_by' => null,
             'empty_data' => $emptyData,
-            'empty_value' => new \Exception(), // deprecated
+            'empty_value' => self::DEPRECATED_EMPTY_VALUE,
             'placeholder' => $placeholder,
             'error_bubbling' => false,
             'compound' => $compound,

src/Symfony/Component/Form/Extension/Core/Type/DateType.php

@@ -183,7 +183,7 @@ public function configureOptions(OptionsResolver $resolver)
         };
 
         $placeholderNormalizer = function (Options $options, $placeholder) use ($placeholderDefault) {
-            if (!is_object($options['empty_value']) || !$options['empty_value'] instanceof \Exception) {
+            if (ChoiceType::DEPRECATED_EMPTY_VALUE !== $options['empty_value']) {
                 @trigger_error('The form option "empty_value" is deprecated since version 2.6 and will be removed in 3.0. Use "placeholder" instead.', E_USER_DEPRECATED);
 
                 $placeholder = $options['empty_value'];
@@ -218,7 +218,7 @@ public function configureOptions(OptionsResolver $resolver)
             'format' => $format,
             'model_timezone' => null,
             'view_timezone' => null,
-            'empty_value' => new \Exception(), // deprecated
+            'empty_value' => ChoiceType::DEPRECATED_EMPTY_VALUE,
             'placeholder' => $placeholder,
             'html5' => true,
             // Don't modify \DateTime classes by reference, we treat

src/Symfony/Component/Form/Extension/Core/Type/TimeType.php

@@ -184,7 +184,7 @@ public function configureOptions(OptionsResolver $resolver)
         };
 
         $placeholderNormalizer = function (Options $options, $placeholder) use ($placeholderDefault) {
-            if (!is_object($options['empty_value']) || !$options['empty_value'] instanceof \Exception) {
+            if (ChoiceType::DEPRECATED_EMPTY_VALUE !== $options['empty_value']) {
                 @trigger_error('The form option "empty_value" is deprecated since version 2.6 and will be removed in 3.0. Use "placeholder" instead.', E_USER_DEPRECATED);
 
                 $placeholder = $options['empty_value'];
@@ -216,7 +216,7 @@ public function configureOptions(OptionsResolver $resolver)
             'with_seconds' => false,
             'model_timezone' => null,
             'view_timezone' => null,
-            'empty_value' => new \Exception(), // deprecated
+            'empty_value' => ChoiceType::DEPRECATED_EMPTY_VALUE,
             'placeholder' => $placeholder,
             'html5' => true,
             // Don't modify \DateTime classes by reference, we treat