diff -u b/core/modules/filter/filter.module b/core/modules/filter/filter.module
--- b/core/modules/filter/filter.module
+++ b/core/modules/filter/filter.module
@@ -105,6 +105,7 @@
   );
   $type['processed_text'] = array(
     '#text' => '',
+    '#format' => NULL,
     '#filter_types_to_skip' => array(),
     '#langcode' => '',
     '#pre_render' => array(
@@ -278,13 +279,13 @@
  *
  * @param string $text
  *   The text to be filtered.
- * @param string|null $format_id
- *   (optional) The machine name of the filter format to be used to filter the
- *   text. Defaults to the fallback format. See filter_fallback_format().
+ * @param string $format_id
+ *   The machine name of the filter format to be used to filter the text.
  * @param string $langcode
  *   (optional) The language code of the text to be filtered, e.g. 'en' for
- *   English. This allows filters to be language-aware so language-specific
- *   text replacement can be implemented. Defaults to an empty string.
+ *   English. This allows filters to be language-aware so language-specific text
+ *   replacement can be implemented. Defaults to
+ *   Drupal\Core\Language\LanguageInterface::LANGCODE_NOT_SPECIFIED.
  * @param array $filter_types_to_skip
  *   (optional) An array of filter types to skip, or an empty array (default)
  *   to skip no filter types. All of the format's filters will be applied,
@@ -299,20 +300,20 @@
  *
  * @ingroup sanitization
  */
-function check_markup($text, $format_id = NULL, $langcode = '', $filter_types_to_skip = array()) {
+function check_markup($text, $format_id, $langcode = LanguageInterface::LANGCODE_NOT_SPECIFIED, $filter_types_to_skip = array()) {
   $build = array(
     '#type' => 'processed_text',
     '#text' => $text,
  *
  * @param string $text
  *   The text to be filtered.
- * @param string $format_id
- *   The machine name of the filter format to be used to filter the text.
+ * @param string|null $format_id
+ *   (optional) The machine name of the filter format to be used to filter the
+ *   text. Defaults to the fallback format. See filter_fallback_format().
  * @param string $langcode
  *   (optional) The language code of the text to be filtered, e.g. 'en' for
- *   English. This allows filters to be language-aware so language-specific text
- *   replacement can be implemented. Defaults to
- *   Drupal\Core\Language\LanguageInterface::LANGCODE_NOT_SPECIFIED.
+ *   English. This allows filters to be language-aware so language-specific
+ *   text replacement can be implemented. Defaults to an empty string.
  * @param array $filter_types_to_skip
  *   (optional) An array of filter types to skip, or an empty array (default)
  *   to skip no filter types. All of the format's filters will be applied,
@@ -327,7 +328,7 @@
  *
  * @ingroup sanitization
  */
-function check_markup($text, $format_id, $langcode = LanguageInterface::LANGCODE_NOT_SPECIFIED, $filter_types_to_skip = array()) {
+function check_markup($text, $format_id = NULL, $langcode = '', $filter_types_to_skip = array()) {
   $build = array(
     '#type' => 'processed_text',
     '#text' => $text,
diff -u b/core/modules/filter/src/Element/ProcessedText.php b/core/modules/filter/src/Element/ProcessedText.php
--- b/core/modules/filter/src/Element/ProcessedText.php
+++ b/core/modules/filter/src/Element/ProcessedText.php
@@ -27,7 +27,6 @@
     $class = get_class($this);
     return array(
       '#text' => '',
-      '#format' => NULL,
       '#filter_types_to_skip' => array(),
       '#langcode' => '',
       '#pre_render' => array(
@@ -65,7 +64,7 @@
    *   The passed-in element with the filtered text in '#markup'.
    *
    * @throws |InvalidArgumentException
-   *   When no $format_id is specified.
+   *   When $element['#format'] is NULL.
    *
    * @ingroup sanitization
    */
@@ -76,7 +75,7 @@
     $langcode = $element['#langcode'];
 
     if (!isset($format_id)) {
-      throw new \InvalidArgumentException('Format ID is not set');
+      throw new \InvalidArgumentException('$element[\'#format\'] must not be NULL.');
     }
     // If the requested text format does not exist, the text cannot be filtered.
     /** @var \Drupal\filter\Entity\FilterFormat $format **/
only in patch2:
unchanged:
--- a/core/modules/comment/src/CommentViewBuilder.php
+++ b/core/modules/comment/src/CommentViewBuilder.php
@@ -157,7 +157,7 @@ public function buildComponents(array &$build, array $entities, array $displays,
         $build[$id]['signature'] = array(
           '#type' => 'processed_text',
           '#text' => $account->getSignature(),
-          '#format' => $account->getSignatureFormat(),
+          '#format' => $account->getSignatureFormat() ? $account->getSignatureFormat() : filter_fallback_format(),
           '#langcode' => $entity->language()->getId(),
         );
       }
only in patch2:
unchanged:
--- a/core/modules/text/src/Plugin/Field/FieldFormatter/TextDefaultFormatter.php
+++ b/core/modules/text/src/Plugin/Field/FieldFormatter/TextDefaultFormatter.php
@@ -38,7 +38,7 @@ public function viewElements(FieldItemListInterface $items) {
       $elements[$delta] = array(
         '#type' => 'processed_text',
         '#text' => $item->value,
-        '#format' => $item->format,
+        '#format' => isset($item->format) ? $item->format : filter_fallback_format(),
         '#langcode' => $item->getLangcode(),
       );
     }
only in patch2:
unchanged:
--- a/core/modules/text/src/Plugin/Field/FieldFormatter/TextTrimmedFormatter.php
+++ b/core/modules/text/src/Plugin/Field/FieldFormatter/TextTrimmedFormatter.php
@@ -85,7 +85,7 @@ public function viewElements(FieldItemListInterface $items) {
       $elements[$delta] = array(
         '#type' => 'processed_text',
         '#text' => NULL,
-        '#format' => $item->format,
+        '#format' => isset($item->format) ? $item->format : filter_fallback_format(),
         '#langcode' => $item->getLangcode(),
       );
 
only in patch2:
unchanged:
--- a/core/modules/views/src/Plugin/views/area/Text.php
+++ b/core/modules/views/src/Plugin/views/area/Text.php
@@ -63,7 +63,7 @@ public function render($empty = FALSE) {
       return array(
         '#type' => 'processed_text',
         '#text' => $this->tokenizeValue($this->options['content']),
-        '#format' => $format,
+        '#format' => isset($format) ? $format : filter_fallback_format(),
       );
     }