Fix failing test

Author: jbman223

doc/source/whatsnew/v1.0.0.rst

@@ -86,7 +86,7 @@ You can use the alias ``"string"`` as well.
    s
 
 The usual string accessor methods work. Where appropriate, the return type
-of the Series or columns of a DataFrame will also have string dtype.
+of the Series or columns of a DataFrame will also have string dtype. (:issue:`29975`)
 
 .. ipython:: python
 
@@ -853,7 +853,6 @@ Other
 - Fix :class:`AbstractHolidayCalendar` to return correct results for
   years after 2030 (now goes up to 2200) (:issue:`27790`)
 - Bug in :meth:`Series.count` raises if use_inf_as_na is enabled (:issue:`29478`)
-- Bug in :meth:`DaataFrame.to_csv` when supplied a series with a ``dtype="string"`` and a ``na_rep``, the ``na_rep`` was being truncated to 2 characters. (:issue:`29975`)
 
 .. _whatsnew_1000.contributors:
 

pandas/core/internals/blocks.py

@@ -657,8 +657,11 @@ def to_native_types(self, slicer=None, na_rep="nan", quoting=None, **kwargs):
         mask = isna(values)
 
         if not self.is_object and not quoting:
-            itemsize = writers.word_len(na_rep)
-            values = values.astype("<U{size}".format(size=itemsize))
+            try:
+                itemsize = writers.word_len(na_rep)
+                values = values.astype("<U{size}".format(size=itemsize))
+            except:
+                values = np.array(values, dtype="object")
         else:
             values = np.array(values, dtype="object")
 
@@ -1775,10 +1778,10 @@ def to_native_types(self, slicer=None, na_rep="nan", quoting=None, **kwargs):
 
         try:
             values[mask] = na_rep
-            values = values.astype(str)
         except Exception:
             # eg SparseArray does not support setitem, needs to be converted to ndarray
             return super().to_native_types(slicer, na_rep, quoting, **kwargs)
+        values = values.astype(str)
 
         # we are expected to return a 2-d ndarray
         return values.reshape(1, len(values))