[BUG] Cannot insert a cudf.NA into a DataFrame

[sarahyurick]

In Pandas, I can do the following:

import pandas as pd
x = pd.DataFrame({'a':[1,2,3]})
x['b'] = pd.NA
x
   a     b
0  1  <NA>
1  2  <NA>
2  3  <NA>

However, with cuDF I get the following error:

import cudf
x = cudf.DataFrame({'a':[1,2,3]})
x['b'] = cudf.NA
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
/tmp/ipykernel_33816/3347028048.py in <module>
      1 import pandas as pd
      2 
----> 3 x['b'] = cudf.NA

~/miniconda3/envs/cudf_dev/lib/python3.8/contextlib.py in inner(*args, **kwds)
     73         def inner(*args, **kwds):
     74             with self._recreate_cm():
---> 75                 return func(*args, **kwds)
     76         return inner
     77 

~/miniconda3/envs/cudf_dev/lib/python3.8/site-packages/cudf/core/dataframe.py in __setitem__(self, arg, value)
    764                     # disc. with pandas here
    765                     # pandas raises key error here
--> 766                     self.insert(len(self._data), arg, value)
    767 
    768         elif can_convert_to_column(arg):

~/miniconda3/envs/cudf_dev/lib/python3.8/contextlib.py in inner(*args, **kwds)
     73         def inner(*args, **kwds):
     74             with self._recreate_cm():
---> 75                 return func(*args, **kwds)
     76         return inner
     77 

~/miniconda3/envs/cudf_dev/lib/python3.8/site-packages/cudf/core/dataframe.py in insert(self, loc, name, value)
   3080 
   3081         if _is_scalar_or_zero_d_array(value):
-> 3082             value = utils.scalar_broadcast_to(value, len(self))
   3083 
   3084         if len(self) == 0:

~/miniconda3/envs/cudf_dev/lib/python3.8/site-packages/cudf/utils/utils.py in scalar_broadcast_to(scalar, size, dtype)
     69 
     70     scalar = to_cudf_compatible_scalar(scalar, dtype=dtype)
---> 71     dtype = scalar.dtype
     72 
     73     if np.dtype(dtype).kind in ("O", "U"):

AttributeError: 'NAType' object has no attribute 'dtype'