From 49298ce6965b61f92688021f1362a78312e2a579 Mon Sep 17 00:00:00 2001
From: Rachel Fenichel <fenichel@google.com>
Date: Tue, 24 Jul 2018 16:44:15 -0700
Subject: [PATCH] Don't break on a null mutation

---
 core/insertion_marker_manager.js | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/core/insertion_marker_manager.js b/core/insertion_marker_manager.js
index ade8c3d432..08dd6611e0 100644
--- a/core/insertion_marker_manager.js
+++ b/core/insertion_marker_manager.js
@@ -257,7 +257,9 @@ Blockly.InsertionMarkerManager.prototype.createMarkerBlock_ = function(sourceBlo
     result.setInsertionMarker(true, sourceBlock.width);
     if (sourceBlock.mutationToDom) {
       var oldMutationDom = sourceBlock.mutationToDom();
-      result.domToMutation(oldMutationDom);
+      if (oldMutationDom) {
+        result.domToMutation(oldMutationDom);
+      }
     }
     result.initSvg();
   } finally {