BUG: replacement works for object but not string dtype

[yunkypunky]

• I have checked that this issue has not already been reported.

• I have confirmed this bug exists on the latest version of pandas.

• (optional) I have confirmed this bug exists on the master branch of pandas.

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Code Sample

import pandas as pd
import numpy as np

a = pd.DataFrame({'a': ['a', 'b', 'c'], 'b': ['d', '', '']}, dtype='object')
b = pd.DataFrame({'a': ['a', 'b', 'c'], 'b': ['d', '', '']}, dtype='string')

print(a)
a.replace(r'^\s*$', pd.NA, regex=True, inplace=True)
print(a)

print(b)
b.replace(r'^\s*$', pd.NA, regex=True, inplace=True)
print(b)

Problem description

replace(r'^\s*$', pd.NA, regex=True, inplace=True) works on object dtype, but not on stringdtype

Expected Output

Same on both replacement

Output of pd.show_versions()

[paste the output of pd.show_versions() here leaving a blank line after the details tag]

[yunkypunky]

replace(r'^\s*$',pd.NA,regex=True,inplace=True) works on object dtype, but not on stringdtype

Code sample:

import pandas as pd
import numpy as np

a = pd.DataFrame({'a':['a','b','c'],'b':['d','','']},dtype='object')
b = pd.DataFrame({'a':['a','b','c'],'b':['d','','']},dtype='string')

display(a[a['b']==''])
a.replace(r'^\s*$',pd.NA,regex=True,inplace=True)
display(a[a['b']==''])

display(b[b['b']==''])
b.replace(r'^\s*$',pd.NA,regex=True,inplace=True)
display(b[b['b']==''])

Expected output:
Same on both replacement

[dsaxton]

@yunkypunky Thanks for the report. This could be a real bug (haven't looked too closely yet) so I think it's worth leaving open for now.