Add isSelected() helper to form field

Fixes an issue where dropdown NULL and 0 are treated as the same
Fixes #2612

modules/backend/classes/FormField.php

@@ -351,6 +351,20 @@ class FormField
         return $this;
     }
 
+    /**
+     * Determine if the provided value matches this field's value.
+     * @param string $value
+     * @return bool
+     */
+    public function isSelected($value = true)
+    {
+        if ($this->value === null) {
+            return false;
+        }
+
+        return (string) $value === (string) $this->value;
+    }
+
     /**
      * Sets the attributes for this field in a given position.
      * - field: Attributes are added to the form field element (input, select, textarea, etc)

modules/backend/widgets/form/partials/_field_balloon-selector.htm

@@ -9,7 +9,7 @@
     <?= $field->getAttributes() ?>>
     <ul>
         <?php foreach ($fieldOptions as $value => $text): ?>
-            <li data-value="<?= e($value) ?>" class="<?= $value == $field->value ? 'active' : '' ?>"><?= e(trans($text)) ?></li>
+            <li data-value="<?= e($value) ?>" class="<?= $field->isSelected($value) ? 'active' : '' ?>"><?= e(trans($text)) ?></li>
         <?php endforeach ?>
     </ul>
 

modules/backend/widgets/form/partials/_field_checkbox.htm

@@ -11,7 +11,7 @@
         name="<?= $field->getName() ?>"
         value="1"
         <?= $this->previewMode ? 'disabled="disabled"' : '' ?>
-        <?= $field->value == 1 ? 'checked="checked"' : '' ?>
+        <?= $field->isSelected() ? 'checked="checked"' : '' ?>
         <?= $field->getAttributes() ?>>
 
     <label for="<?= $field->getId() ?>">

modules/backend/widgets/form/partials/_field_dropdown.htm

@@ -22,7 +22,7 @@
                 if (!is_array($option)) $option = [$option];
             ?>
             <option
-                <?= $value == $field->value ? 'selected="selected"' : '' ?>
+                <?= $field->isSelected($value) ? 'selected="selected"' : '' ?>
                 <?php if (isset($option[1])): ?>data-<?=strpos($option[1],'.')?'image':'icon'?>="<?= $option[1] ?>"<?php endif ?>
                 value="<?= $value ?>"
             ><?= e(trans($option[0])) ?></option>

modules/backend/widgets/form/partials/_field_radio.htm

@@ -19,7 +19,7 @@
                 name="<?= $field->getName() ?>"
                 value="<?= $value ?>"
                 type="radio"
-                <?= $field->value == $value ? 'checked="checked"' : '' ?>
+                <?= $field->isSelected($value) ? 'checked="checked"' : '' ?>
                 <?= $this->previewMode ? 'disabled="disabled"' : '' ?>
                 <?= $field->getAttributes() ?>>