core/modules/rest/src/Plugin/rest/resource/EntityResource.php | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/core/modules/rest/src/Plugin/rest/resource/EntityResource.php b/core/modules/rest/src/Plugin/rest/resource/EntityResource.php
index 6f18e7d..4b6febc 100644
--- a/core/modules/rest/src/Plugin/rest/resource/EntityResource.php
+++ b/core/modules/rest/src/Plugin/rest/resource/EntityResource.php
@@ -230,6 +230,12 @@ public function patch(EntityInterface $original_entity, EntityInterface $entity
     // Overwrite the received fields.
     foreach ($entity->_restSubmittedFields as $field_name) {
       $field = $entity->get($field_name);
+      // It is not possible to set the language to NULL as it is automatically
+      // re-initialized. As it must not be empty, skip it if it is.
+      // @todo Remove in https://www.drupal.org/project/drupal/issues/2933408.
+      if ($entity->getEntityType()->hasKey('langcode') && $field_name === $entity->getEntityType()->getKey('langcode') && $field->isEmpty()) {
+        continue;
+      }
       if ($this->checkPatchFieldAccess($original_entity->get($field_name), $field)) {
         $original_entity->set($field_name, $field->getValue());
       }