Error when no paragraph was matched: torch.cat(): expected a non-empty list of Tensors

[AnywhereSoftware]

To better understand the behavior of pids, I've added and removed (IndexUpdater.remove) short paragraphs.
It started crashing with one specific query. It looks like it fails when no pid was matched.
Code:

with Run().context(RunConfig(experiment='notebook')):
searcher = Searcher(index=index_name)
results = searcher.search("7", k=4, filter_fn=None)

Error:
File "/home/erel/PycharmProjects/colbert_test/test.py", line 78, in search
results = searcher.search("7", k=4, filter_fn=None)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/erel/python_env/lib/python3.12/site-packages/colbert/searcher.py", line 67, in search
return self.dense_search(Q, k, filter_fn=filter_fn, pids=pids)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/erel/python_env/lib/python3.12/site-packages/colbert/searcher.py", line 129, in dense_search
pids, scores = self.ranker.rank(self.config, Q, filter_fn=filter_fn, pids=pids)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/erel/python_env/lib/python3.12/site-packages/colbert/search/index_storage.py", line 104, in rank
scores, pids = self.score_pids(config, Q, pids, centroid_scores)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/erel/python_env/lib/python3.12/site-packages/colbert/search/index_storage.py", line 148, in score_pids
approx_scores = torch.cat(approx_scores, dim=0)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
RuntimeError: torch.cat(): expected a non-empty list of Tensors