Error when updating index

Traceback:
Traceback (most recent call last):
File "/usr/local/lib/python3.9/dist-packages/celery_haystack/tasks.py", line 131, in _run_one
current_index.update_object(instance, using=using)
File "/usr/local/lib/python3.9/dist-packages/haystack/indexes.py", line 324, in update_object
backend.update(self, [instance])
File "/usr/local/lib/python3.9/dist-packages/haystack/backends/whoosh_backend.py", line 288, in update
writer.commit()
File "/usr/local/lib/python3.9/dist-packages/whoosh/writing.py", line 1037, in commit
self.writer.commit(*args, **kwargs)
File "/usr/local/lib/python3.9/dist-packages/whoosh/writing.py", line 922, in commit
finalsegments = self._merge_segments(mergetype, optimize, merge)
File "/usr/local/lib/python3.9/dist-packages/whoosh/writing.py", line 827, in _merge_segments
return mergetype(self, self.segments)
File "/usr/local/lib/python3.9/dist-packages/whoosh/writing.py", line 101, in MERGE_SMALL
writer.add_reader(reader)
File "/usr/local/lib/python3.9/dist-packages/whoosh/writing.py", line 709, in add_reader
docmap = self.write_per_doc(fieldnames, reader)
File "/usr/local/lib/python3.9/dist-packages/whoosh/writing.py", line 678, in write_per_doc
for docnum, stored in reader.iter_docs():
File "/usr/local/lib/python3.9/dist-packages/whoosh/codec/base.py", line 419, in iter_docs
yield docnum, self.stored_fields(docnum)
File "/usr/local/lib/python3.9/dist-packages/whoosh/codec/whoosh3.py", line 495, in stored_fields
v = reader[docnum]
TypeError: 'NoneType' object is not subscriptable

added part::backend prio::1 source::customer type::bug labels