Cannot edit any doctype

So it seems out of the sudden, editing doctypes is not possible anymore.

The traceback is this:

Form Dict: {
 "action": "Save",
 "cmd": "",
 "doc": "{\"allow_import\":0,\"creation\":\"2019-08-27 10:43:26.462941\",\"search_fields\":\"\",\"module\":\"Guests\",\"track_seen\":1,\"sort$
Request Error
Traceback (most recent call last):
  File "/home/frappe/frappe-bench/apps/frappe/frappe/", line 60, in application
    response = frappe.api.handle()
  File "/home/frappe/frappe-bench/apps/frappe/frappe/", line 55, in handle
    return frappe.handler.handle()
  File "/home/frappe/frappe-bench/apps/frappe/frappe/", line 21, in handle
    data = execute_cmd(cmd)
  File "/home/frappe/frappe-bench/apps/frappe/frappe/", line 56, in execute_cmd
    return, **frappe.form_dict)
  File "/home/frappe/frappe-bench/apps/frappe/frappe/", line 1036, in call
    return fn(*args, **newargs)
  File "/home/frappe/frappe-bench/apps/frappe/frappe/desk/form/", line 22, in savedocs
  File "/home/frappe/frappe-bench/apps/frappe/frappe/model/", line 271, in save
    return self._save(*args, **kwargs)
  File "/home/frappe/frappe-bench/apps/frappe/frappe/model/", line 310, in _save
  File "/home/frappe/frappe-bench/apps/frappe/frappe/model/", line 463, in _validate
  File "/home/frappe/frappe-bench/apps/frappe/frappe/model/", line 656, in _sanitize_content
    or self.docstatus==2
AttributeError: 'NoneType' object has no attribute 'fieldtype' 

Anyone else experiencing this issue on the latest version v12 ?

Yes having the same issue on Frappe V12.0.10
I don’t have ERPNext installed, just Frappe. Since this is a test env, I can temporally go around by doing a bench reinstall but the issue resurface after a few saves

It seems there is a blank comment being added to the doctype

Delete that comment and it should work.