diff --git a/core/modules/views/src/Plugin/views/row/OpmlFields.php b/core/modules/views/src/Plugin/views/row/OpmlFields.php
index 4654bca..a2ddf43 100644
--- a/core/modules/views/src/Plugin/views/row/OpmlFields.php
+++ b/core/modules/views/src/Plugin/views/row/OpmlFields.php
@@ -212,6 +212,9 @@ public function render($row) {
    *   The index count of the row as expected by views_plugin_style::getField().
    * @param $field_id
    *   The ID assigned to the required field in the display.
+   *
+   * @return string
+   *   The rendered field value.
    */
   public function getField($index, $field_id) {
     if (empty($this->view->style_plugin) || !is_object($this->view->style_plugin) || empty($field_id)) {
diff --git a/core/modules/views/src/Plugin/views/row/RssFields.php b/core/modules/views/src/Plugin/views/row/RssFields.php
index 25a75d1..1189826 100644
--- a/core/modules/views/src/Plugin/views/row/RssFields.php
+++ b/core/modules/views/src/Plugin/views/row/RssFields.php
@@ -197,6 +197,10 @@ public function render($row) {
    *   The index count of the row as expected by views_plugin_style::getField().
    * @param $field_id
    *   The ID assigned to the required field in the display.
+   *
+   * @return string|null|\Drupal\Component\Render\MarkupInterface
+   *   An empty string if there is no style plugin, or the field ID is empty.
+   *   And NULL if the field is actually empty otherwise MarkupInterface object.
    */
   public function getField($index, $field_id) {
     if (empty($this->view->style_plugin) || !is_object($this->view->style_plugin) || empty($field_id)) {