Traceback (most recent call last):


 "<stdin>", line 1, in <module>


 "./venv/pandas-1/lib64/python3.8/site-packages/pandas/core/groupby/groupby.py", line 539, in __len__

return len(self.groups)


 "./venv/pandas-1/lib64/python3.8/site-packages/pandas/core/groupby/groupby.py", line 558, in groups

return self.grouper.groups


 "pandas/_libs/properties.pyx", line 33, in pandas._libs.properties.CachedProperty.__get__


 "./venv/pandas-1/lib64/python3.8/site-packages/pandas/core/groupby/ops.py", line 257, in groups

return self.groupings[0].groups


 "pandas/_libs/properties.pyx", line 33, in pandas._libs.properties.CachedProperty.__get__


 "./venv/pandas-1/lib64/python3.8/site-packages/pandas/core/groupby/grouper.py", line 598, in groups

return self.index.groupby(Categorical.from_codes(self.codes, self.group_index))


 "./venv/pandas-1/lib64/python3.8/site-packages/pandas/core/arrays/categorical.py", line 606, in from_codes

dtype = CategoricalDtype._from_values_or_dtype(


 "./venv/pandas-1/lib64/python3.8/site-packages/pandas/core/dtypes/dtypes.py", line 365, in _from_values_or_dtype

dtype = CategoricalDtype(categories, ordered)


 "./venv/pandas-1/lib64/python3.8/site-packages/pandas/core/dtypes/dtypes.py", line 252, in __init__

self._finalize(categories, ordered, fastpath=False)


 "./venv/pandas-1/lib64/python3.8/site-packages/pandas/core/dtypes/dtypes.py", line 406, in _finalize

categories = self.validate_categories(categories, fastpath=fastpath)


 "./venv/pandas-1/lib64/python3.8/site-packages/pandas/core/dtypes/dtypes.py", line 579, in validate_categories

raise ValueError("Categorical categories cannot be null")
ValueError: Categorical categories cannot be null

Traceback (most recent call last):


 "C:\Python\anaconda3\lib\site-packages\spyder\widgets\variableexplorer\dataframeeditor.py", line 295, in data

return to_qvariant(to_text_string(value))


 "C:\Python\anaconda3\lib\site-packages\spyder\py3compat.py", line 140, in to_text_string

return str(obj)


 "C:\Python\anaconda3\lib\site-packages\pandas\core\base.py", line 59, in __str__

return self.__unicode__()


 "C:\Python\anaconda3\lib\site-packages\pandas\core\frame.py", line 636, in __unicode__

line_width=width, show_dimensions=show_dimensions)


 "C:\Python\anaconda3\lib\site-packages\pandas\core\frame.py", line 1675, in to_string

formatter.to_string()


 "C:\Python\anaconda3\lib\site-packages\pandas\io\formats\format.py", line 597, in to_string

strcols = self._to_str_columns()


 "C:\Python\anaconda3\lib\site-packages\pandas\io\formats\format.py", line 537, in _to_str_columns

max_len = max(np.max([self.adj.len(x) for x in fmt_values]),


 "C:\Python\anaconda3\lib\site-packages\numpy\core\fromnumeric.py", line 2320, in amax

out=out, **kwargs)


 "C:\Python\anaconda3\lib\site-packages\numpy\core\_methods.py", line 26, in _amax

return umr_maximum(a, axis, None, out, keepdims)
ValueError: zero-size array to reduction operation maximum which has no identity
