Unpickled StringArray with pd.NA raises ValueError

[bjonen]

Code Sample, a copy-pastable example if possible

import pandas as pd
import pickle
df = pd.Series(['abc'] +  [pd.NA]*60, dtype='string')
serialized = pickle.dumps(df)
unserialized = pickle.loads(serialized)
print(unserialized)

Problem description

The unserialized df cannot be printed. Fails with
ValueError: StringArray requires a sequence of strings or pandas.NA

Note that things work fine with less than 60 pd.NA

import pandas as pd
import pickle
df = pd.Series(['abc'] +  [pd.NA]*59, dtype='string')
serialized = pickle.dumps(df)
unserialized = pickle.loads(serialized)
print(unserialized)

Expected Output

Print out simple df

Output of pd.show_versions()

INSTALLED VERSIONS

commit : None
python : 3.6.7.final.0
python-bits : 64
OS : Linux
OS-release : 3.10.0-1062.9.1.el7.x86_64
machine : x86_64
processor :
byteorder : little
LC_ALL : C
LANG : en_US.UTF-8A
LOCALE : None.None

pandas : 1.0.0
numpy : 1.18.1
pytz : 2019.3
dateutil : 2.8.1
pip : 20.0.2
setuptools : 45.2.0.post20200209
Cython : 0.29.15
pytest : 5.3.5
hypothesis : None
sphinx : 2.4.1
blosc : None
feather : None
xlsxwriter : 1.2.7
lxml.etree : 4.5.0
html5lib : None
pymysql : None
psycopg2 : None
jinja2 : 2.11.1
IPython : 7.12.0
pandas_datareader: None
bs4 : None
bottleneck : None
fastparquet : None
gcsfs : None
lxml.etree : 4.5.0
matplotlib : 3.1.3
numexpr : 2.7.1
odfpy : None
openpyxl : None
pandas_gbq : None
pyarrow : 0.16.0
pytables : None
pytest : 5.3.5
pyxlsb : None
s3fs : None
scipy : 1.4.1
sqlalchemy : 1.3.13
tables : 3.6.1
tabulate : None
xarray : 0.15.0
xlrd : 1.2.0
xlwt : 1.3.0
xlsxwriter : 1.2.7
numba : 0.48.0

[MarcoGorelli]

Thanks @bjonen

Seems related to #31847

[TomAugspurger]

I think it's a duplicate of #31847