Disallow empty comments and comments with only whitespaces (#7156)

* fix: disallow empty comments

* fix: avoid full traversal to validate comment

* fix: text

* fix:review

* fix: review

server/routes/api/schema.ts

@@ -2,6 +2,7 @@ import formidable from "formidable";
 import { Node } from "prosemirror-model";
 import { z } from "zod";
 import { ProsemirrorData as TProsemirrorData } from "@shared/types";
+import { ProsemirrorHelper } from "@shared/utils/ProsemirrorHelper";
 import { schema } from "@server/editor";
 
 export const BaseSchema = z.object({
@@ -14,7 +15,7 @@ export const ProsemirrorSchema = z.custom<TProsemirrorData>((val) => {
   try {
     const node = Node.fromJSON(schema, val);
     node.check();
-    return true;
+    return !ProsemirrorHelper.isEmpty(node, schema);
   } catch (_e) {
     return false;
   }