diff --git a/packages/bridge/src/utils/index.ts b/packages/bridge/src/utils/index.ts
index 137a2c4..da1257f 100644
--- a/packages/bridge/src/utils/index.ts
+++ b/packages/bridge/src/utils/index.ts
@@ -6,6 +6,9 @@ import { CollabAction } from '../model'
 export * from './testUtils'
 
 const toJS = (node: any) => {
+  if (node === undefined) {
+    return undefined
+  }
   try {
     return JSON.parse(JSON.stringify(node))
   } catch (e) {