NNDescent.update() fails even for compressed or uncompressed indexes

$ conda install -c conda-forge pynndescent
$ ipython --version
8.0.1
$ python --version
Python 3.9.7

>>> import pynndescent as pynn
>>> pynn.__version__
'0.5.6'

I'm unable to update the index to append new vectors to the existing NN graph, whether or not the initial graph is compressed.
vecs and vecs2 contain 300D GloVe Vectors:

>>> index = NNDescent(vecs, metric="cosine", compressed=False)
>>> index.update(vecs2)
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
Input In [147], in <module>
----> 1 index.update(vecs2)

File ~/anaconda3/envs/nessvec/lib/python3.9/site-packages/pynndescent/pynndescent_.py:1614, in NNDescent.update(self, X)
   1609 rng_state = current_random_state.randint(INT32_MIN, INT32_MAX, 3).astype(
   1610     np.int64
   1611 )
   1612 X = check_array(X, dtype=np.float32, accept_sparse="csr", order="C")
-> 1614 original_order = np.argsort(self._vertex_order)
   1616 if self._is_sparse:
   1617     self._raw_data = sparse_vstack([self._raw_data, X])

AttributeError: 'NNDescent' object has no attribute '_vertex_order'

Start in pynndescent/pynndescent_.py at NNDescent.update(), especially around line 1614 where _vertex_order is accessed. Reproduce the reported 300D GloVe vecs/vecs2 setup for compressed=False and compressed indexes, then verify that update appends vectors without raising AttributeError.