Error exporting/disconnecting pool - 'NoneType' object has no attribute 'split'

Just upgraded my system from FreeNAS 11.3 U5 to TrueNAS-12.0.-U3.1 using the GUI.

My first task was to export my pools but get the following error on both of the 2 pools I have.

Error: Traceback (most recent call last):
File "/usr/local/lib/python3.8/site-packages/middlewared/main.py", line 137, in call_method
result = await self.middleware._call(message['method'], serviceobj, methodobj, params, app=self,
File "/usr/local/lib/python3.8/site-packages/middlewared/main.py", line 1195, in _call
return await methodobj(*prepared_call.args)
File "/usr/local/lib/python3.8/site-packages/middlewared/schema.py", line 973, in nf
return await f(*args, **kwargs)
File "/usr/local/lib/python3.8/site-packages/middlewared/plugins/pool.py", line 1646, in attachments
return await self.middleware.call('pool.dataset.attachments_with_path', pool['path'])
File "/usr/local/lib/python3.8/site-packages/middlewared/main.py", line 1238, in call
return await self._call(
File "/usr/local/lib/python3.8/site-packages/middlewared/main.py", line 1195, in _call
return await methodobj(*prepared_call.args)
File "/usr/local/lib/python3.8/site-packages/middlewared/plugins/pool.py", line 3766, in attachments_with_path
for attachment in await delegate.query(path, True):
File "/usr/local/lib/python3.8/site-packages/middlewared/plugins/s3_/attachments.py", line 21, in query
if query_dataset in (s3_ds, s3_ds.split('/')[0]) or query_dataset.startswith(f'{s3_ds}/'):
AttributeError: 'NoneType' object has no attribute 'split'

There is a thread on the forum with other members reporting the same issue but I've not been able to locate a bug reported here.

https://www.truenas.com/community/threads/cannot-export-pool-with-u3.92538/