diff --git a/core/modules/block/src/BlockForm.php b/core/modules/block/src/BlockForm.php
index 17b402c..079f605 100644
--- a/core/modules/block/src/BlockForm.php
+++ b/core/modules/block/src/BlockForm.php
@@ -344,7 +344,8 @@ public function submitForm(array &$form, FormStateInterface $form_state) {
           ->setValues($values);
         $condition->submitConfigurationForm($form, $condition_values);
         if ($condition instanceof ContextAwarePluginInterface) {
-          $condition->setContextMapping($values['context_mapping']);
+          $context_mapping = isset($values['context_mapping']) ? $values['context_mapping'] : [];
+          $condition->setContextMapping($context_mapping);
         }
         // Update the original form values.
         $form_state->setValue(['visibility', $condition_id], $condition->getConfiguration());