diff --git a/src/Form/IndexAddFieldsForm.php b/src/Form/IndexAddFieldsForm.php
index 078fbb46..7a7f7434 100644
--- a/src/Form/IndexAddFieldsForm.php
+++ b/src/Form/IndexAddFieldsForm.php
@@ -229,10 +229,6 @@ protected function getDatasourceListItem(DatasourceInterface $datasource = NULL)
       $base_url->setOption('query', ['datasource' => $datasource_id_param]);
 
       $item = $this->getPropertiesList($properties, $active_property_path, $base_url, $datasource_id);
-
-      // Sort the retrieved properties by their label.
-      uasort($item, [$this->fieldsHelper, 'sortByFieldLabel']);
-
       $item['#title'] = $datasource ? $datasource->label() : $this->t('General');
       return $item;
     }
@@ -263,9 +259,7 @@ protected function getDatasourceListItem(DatasourceInterface $datasource = NULL)
    *   properties.
    */
   protected function getPropertiesList(array $properties, $active_property_path, Url $base_url, $datasource_id, $parent_path = '', $label_prefix = '') {
-    $list = [
-      '#theme' => 'search_api_form_item_list',
-    ];
+    $list = [];
 
     $active_item = '';
     if ($active_property_path) {
@@ -398,10 +392,37 @@ protected function getPropertiesList(array $properties, $active_property_path, U
       $list[$key] = $item;
     }
 
+    if ($list) {
+      uasort($list, [static::class, 'compareFieldLabels']);
+      $list['#theme'] = 'search_api_form_item_list';
+    }
+
     return $list;
   }
 
   /**
+   * Compares labels of property render arrays.
+   *
+   * Used as an uasort() callback in
+   * \Drupal\search_api\Form\IndexAddFieldsForm::getPropertiesList().
+   *
+   * @param array $a
+   *   First property render array.
+   * @param array $b
+   *   Second property render array.
+   *
+   * @return int
+   *   -1, 0 or 1 if the first array should be considered, respectively, less
+   *   than, equal to or greater than the second.
+   */
+  public static function compareFieldLabels(array $a, array $b) {
+    $a_title = (string) $a['label']['#markup'];
+    $b_title = (string) $b['label']['#markup'];
+
+    return strnatcasecmp($a_title, $b_title);
+  }
+
+  /**
    * {@inheritdoc}
    */
   protected function actions(array $form, FormStateInterface $form_state) {
diff --git a/src/Utility/FieldsHelper.php b/src/Utility/FieldsHelper.php
index dfe92f39..9e612cf4 100644
--- a/src/Utility/FieldsHelper.php
+++ b/src/Utility/FieldsHelper.php
@@ -488,23 +488,4 @@ public function getNewFieldId(IndexInterface $index, $propertyPath) {
     return $fieldId;
   }
 
-  /**
-   * Uasort callback. Compares field labels found in $field['label']['#markup].
-   *
-   * @param mixed $a
-   *   First item for comparison. The compared items should be associative
-   *   arrays that include a ['label']['#markup] key.
-   * @param mixed $b
-   *   Second item for comparison.
-   *
-   * @return int
-   *   The comparison result for uasort().
-   */
-  public function sortByFieldLabel($a, $b) {
-    $a_title = (is_array($a) && isset($a['label']['#markup'])) ? $a['label']['#markup'] : '';
-    $b_title = (is_array($b) && isset($b['label']['#markup'])) ? $b['label']['#markup'] : '';
-
-    return strnatcasecmp($a_title, $b_title);
-  }
-
 }