diff --git a/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/StringItem.php b/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/StringItem.php
index fe7c4f4..5d7564b 100644
--- a/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/StringItem.php
+++ b/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/StringItem.php
@@ -53,7 +53,7 @@ public static function schema(FieldStorageDefinitionInterface $field_definition)
         'value' => array(
           'type' => 'varchar',
           'length' => (int) $field_definition->getSetting('max_length'),
-          'not null' => FALSE,
+          'not null' => $field_definition->isRequired(),
         ),
       ),
     );