diff --git a/src/prosemirror/schema/nodes.ts b/src/prosemirror/schema/nodes.ts
index c99a8292..b7e4d0eb 100644
--- a/src/prosemirror/schema/nodes.ts
+++ b/src/prosemirror/schema/nodes.ts
@@ -21,7 +21,9 @@ const listNodes = {
 
   paragraph: {
     attrs: {
-      align: {default: null},
+      align: {
+        default: '',
+      },
     },
     content: 'inline*',
     group: 'block',