[6.x] Keep blank Dropdown option values

CHANGELOG.md

@@ -238,6 +238,7 @@
 - Fixed a bug where typing in a newly added nested entry’s fields could replace the edit form with a “UI array path … must be a row index” error once the entry autosaved.
 - Fixed a bug where changing a field back to the value it had when the edit page loaded wasn’t autosaved, so field layout elements shown or hidden by conditions based on it didn’t update.
 - Fixed a bug where Table fields’ Date and Time cells, and their default row values, shifted by the site’s UTC offset each time they were saved from the control panel.
+- Fixed bugs where Dropdown fields didn’t preserve blank option values and could show duplicate blank placeholders. ([#20140](https://github.com/craftcms/cms/pull/20140))
 - Fixed a bug where going from one element edit page to another, such as switching sites, opened the next page’s “Revisions” details panel rather than the one that was open.
 - Fixed a bug where viewing an element revision showed three read-only notices, including one about settings changes not being permitted, and no “Revert content from this revision” button. ([#20115](https://github.com/craftcms/cms/pull/20115))
 - Fixed an error that occurred on release pages if one of the release’s drafts belonged to an element that had been deleted, such as along with its section. The draft is now listed as blocked with “The entry has been deleted.”, and can be removed by anyone who can manage the release.

src/Field/BaseOptionsField.php

@@ -189,6 +189,9 @@ public function __construct($config = [])
                     ];
                 } else {
                     unset($option['isOptgroup']);
+                    // Blank cells are posted as null (ConvertEmptyStringsToNull), and null keys don't survive saving
+                    $option['label'] = (string) ($option['label'] ?? '');
+                    $option['value'] = (string) ($option['value'] ?? '');
                     $options[] = $option;
                 }
             }

src/Field/Dropdown.php

@@ -13,6 +13,8 @@
 use CraftCms\Cms\Field\Data\OptionData;
 use CraftCms\Cms\Field\Data\SingleOptionFieldData;
 use CraftCms\Cms\Support\Facades\DeltaRegistry;
+use CraftCms\Cms\Ui\Contracts\Control;
+use CraftCms\Cms\Ui\Controls\Choice;
 
 use function CraftCms\Cms\t;
 
@@ -62,6 +64,19 @@ public function getStatus(ElementInterface $element): ?array
         return parent::getStatus($element);
     }
 
+    #[\Override]
+    public function uiControl(FieldContext $context): Control
+    {
+        $control = parent::uiControl($context);
+
+        // A blank option is encoded as __blank__, so Choice can't tell it supplies its own empty state
+        if ($control instanceof Choice && collect($this->options)->contains(fn (array $option): bool => ($option['value'] ?? null) === '')) {
+            $control->withoutPlaceholder();
+        }
+
+        return $control;
+    }
+
     #[\Override]
     protected function inputHtml(mixed $value, ?ElementInterface $element, bool $inline): string
     {

tests/Feature/Field/OptionsFieldEmptyValueTest.php

@@ -0,0 +1,58 @@
+<?php
+
+declare(strict_types=1);
+
+use CraftCms\Cms\Field\Dropdown;
+use CraftCms\Cms\Field\FieldContext;
+use CraftCms\Cms\Field\Fields;
+
+test('an option saved without a value is treated as a blank option', function () {
+    $field = new Dropdown([
+        'options' => [
+            ['label' => 'None', 'default' => ''],
+            ['label' => 'A', 'value' => 'a', 'default' => ''],
+        ],
+    ]);
+
+    expect($field->options[0]['value'])->toBe('')
+        ->and($field->normalizeValue(null, null)->value)->toBe('');
+});
+
+test('a blank option value posted as null is saved as an empty string', function () {
+    $fields = app(Fields::class);
+
+    $fields->saveField($field = $fields->createField([
+        'type' => Dropdown::class,
+        'name' => 'Dropdown',
+        'handle' => 'dropdown',
+        'options' => [
+            ['label' => 'None', 'value' => null, 'default' => ''],
+            ['label' => 'A', 'value' => 'a', 'default' => ''],
+        ],
+    ]));
+
+    $fields->refreshFields();
+
+    expect($fields->getFieldById($field->id)->getSettings()['options'][0]['value'])->toBe('');
+});
+
+test('a dropdown with its own blank option does not get another one', function () {
+    $field = new Dropdown([
+        'options' => [
+            ['label' => 'Please select', 'value' => '', 'default' => ''],
+            ['label' => 'A', 'value' => 'a', 'default' => ''],
+        ],
+    ]);
+
+    expect($field->uiControl(new FieldContext('value'))->props()['placeholder'])->toBeFalse();
+});
+
+test('a dropdown without a blank option keeps the leading blank', function () {
+    $field = new Dropdown([
+        'options' => [
+            ['label' => 'A', 'value' => 'a', 'default' => ''],
+        ],
+    ]);
+
+    expect($field->uiControl(new FieldContext('value'))->props())->not->toHaveKey('placeholder');
+});