Error when packing anndata object?

[cameronyoungpark]

Hello, I am trying to run mnnpy.mnn_correct on 2 anndata objects. The code works until the last step of packing AnnData and I get the error: AttributeError: Can only use .str accessor with string values!

Here is the output from the function:

Performing cosine normalization...
Starting MNN correct iteration. Reference batch: 0
Step 1 of 1: processing batch 1
  Looking for MNNs...
  Computing correction vectors...
  Adjusting variance...
  Applying correction...
MNN correction complete. Gathering output...
Packing AnnData object...
/home/cyp2111_columbia_edu/anaconda3/lib/python3.8/site-packages/anndata/_core/anndata.py:1755: FutureWarning: The AnnData.concatenate method is deprecated in favour of the anndata.concat function. Please use anndata.concat instead.

See the tutorial for concat at: https://anndata.readthedocs.io/en/latest/concatenation.html
  warnings.warn(
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-7-f5b1f9f9bdff> in <module>
      2 import mnnpy
      3 
----> 4 corrected = mnnpy.mnn_correct(ad21, ad20)
      5 adata = corrected[0]

~/anaconda3/lib/python3.8/site-packages/mnnpy/mnn.py in mnn_correct(var_index, var_subset, batch_key, index_unique, batch_categories, k, sigma, cos_norm_in, cos_norm_out, svd_dim, var_adj, compute_angle, mnn_order, svd_mode, do_concatenate, save_raw, n_jobs, *datas, **kwargs)
    127         print('Packing AnnData object...')
    128         if do_concatenate:
--> 129             adata = AnnData.concatenate(*datas, batch_key=batch_key,
    130                                         batch_categories=batch_categories,
    131                                         index_unique=index_unique)

~/anaconda3/lib/python3.8/site-packages/anndata/_core/anndata.py in concatenate(self, join, batch_key, batch_categories, uns_merge, index_unique, fill_value, *adatas)
   1806             :,
   1807             (
-> 1808                 out.var.columns.str.extract(pat, expand=False)
   1809                 .fillna("")
   1810                 .argsort(kind="stable")

~/anaconda3/lib/python3.8/site-packages/pandas/core/accessor.py in __get__(self, obj, cls)
    222             # we're accessing the attribute of the class, i.e., Dataset.geo
    223             return self._accessor
--> 224         accessor_obj = self._accessor(obj)
    225         # Replace the property with the accessor object. Inspired by:
    226         # https://www.pydanny.com/cached-property.html

~/anaconda3/lib/python3.8/site-packages/pandas/core/strings/accessor.py in __init__(self, data)
    179         from pandas.core.arrays.string_ import StringDtype
    180 
--> 181         self._inferred_dtype = self._validate(data)
    182         self._is_categorical = is_categorical_dtype(data.dtype)
    183         self._is_string = isinstance(data.dtype, StringDtype)

~/anaconda3/lib/python3.8/site-packages/pandas/core/strings/accessor.py in _validate(data)
    233 
    234         if inferred_dtype not in allowed_types:
--> 235             raise AttributeError("Can only use .str accessor with string values!")
    236         return inferred_dtype
    237 

AttributeError: Can only use .str accessor with string values!

Has anyone encountered this and if so, does anyone know how I can fix this? The datatypes of the obs and vars in the individual anndata objects are strings, so do not know what this is referring to