import pyarrow as pa

fields = [('b', pa.null()),('g', pa.string())]
dtype = pa.list_(pa.struct(fields))
arr  = pa.array([[{'b': None, 'g': None}, {'b': None, 'g': 'moo'}]], type=dtype)
carr = pa.chunked_array(arr)
ext_arr = carr.cast(dtype, safe=True)
print(ext_arr) # prints Invalid array but no exception
print(len(ext_arr)) # Len is 1
print(ext_arr[0]) # Raises ArrowIndexError