diff -u b/core/modules/migrate/src/Plugin/migrate/process/StaticMap.php b/core/modules/migrate/src/Plugin/migrate/process/StaticMap.php
--- b/core/modules/migrate/src/Plugin/migrate/process/StaticMap.php
+++ b/core/modules/migrate/src/Plugin/migrate/process/StaticMap.php
@@ -35,7 +35,7 @@
     }
     $new_value = NestedArray::getValue($this->configuration['map'], $new_value, $key_exists);
     if (!$key_exists) {
-      if (isset($this->configuration['default_value']) || array_key_exists('default_value', $this->configuration)) {
+      if (array_key_exists('default_value', $this->configuration)) {
         if (!empty($this->configuration['bypass'])) {
           throw new MigrateException('Setting both default_value and bypass is invalid.');
         }