Fixed bug to make it possible to save "0" as a mask value.

Closes #3335413

src/Helper/ElementHelper.php

@@ -27,21 +27,23 @@ class ElementHelper implements ElementHelperInterface {
    * {@inheritdoc}
    */
   public static function processElement(array &$element, FormStateInterface $form_state, array &$complete_form) {
-    if (!empty($element['#mask']['value'])) {
+    if (isset($element['#mask']['value']) && $element['#mask']['value'] !== '') {
       // Adds HTML attributes to the element.
       foreach ($element['#mask'] as $option => $value) {
-        if (!empty($value)) {
-          // Appends the option name to the attribute name.
-          $attr = "data-mask-$option";
+        if ($option !== 'value' && empty($value)) {
+          continue;
+        }
 
-          // Except for the value, all other options are booleans.
-          if ($option != 'value') {
-            $value = $value ? 'true' : 'false';
-          }
+        // Appends the option name to the attribute name.
+        $attr = "data-mask-$option";
 
-          // Adds the attribute.
-          $element['#attributes'][$attr] = is_string($value) ? $value : (string) $value;
+        // Except for the value, all other options are booleans.
+        if ($option != 'value') {
+          $value = $value ? 'true' : 'false';
         }
+
+        // Adds the attribute.
+        $element['#attributes'][$attr] = is_string($value) ? $value : (string) $value;
       }
 
       // Attaches the JavaScript library and settings.