diff --git a/src/ReferenceUpgrader.php b/src/ReferenceUpgrader.php
index e533d7e20bd088eebbe4033189b05903e1548c9e..9205d2d79e5058bbded14e25054bb1418d88a650 100644
--- a/src/ReferenceUpgrader.php
+++ b/src/ReferenceUpgrader.php
@@ -29,15 +29,9 @@ final class ReferenceUpgrader {
    * Registers entities.
    */
   public function registerEntity(EntityInterface $entity) {
-    $entityId = $entity->id() ?? $this->throwNeedsId();
-    $this->entities[$entity->getEntityTypeId()][$entityId] = $entity;
-  }
-
-  /**
-   * Throws exceptions on trying to register entities without id.
-   */
-  private function throwNeedsId() {
-    throw new \RuntimeException("Can only register entity with ID.");
+    if ($entityId = $entity->id()) {
+      $this->entities[$entity->getEntityTypeId()][$entityId] = $entity;
+    }
   }
 
   /**