do not replace all nulls with NaN-string

Author: realead

pandas/core/indexes/base.py

@@ -1392,11 +1392,12 @@ def _format_with_header(self, header: list[str_t], na_rep: str_t) -> list[str_t]
             result = [pprint_thing(x, escape_chars=("\t", "\r", "\n")) for x in values]
 
             # could have nans
-            mask = isna(values)
-            if mask.any():
-                result_arr = np.array(result)
-                result_arr[mask] = na_rep
-                result = result_arr.tolist()
+            if na_rep is not None:
+                mask = isna(values)
+                if mask.any():
+                    result_arr = np.array(result)
+                    result_arr[mask] = na_rep
+                    result = result_arr.tolist()
         else:
             result = trim_front(format_array(values, None, justify="left"))
         return header + result

pandas/io/formats/format.py

@@ -366,10 +366,10 @@ def _get_formatted_index(self) -> tuple[list[str], bool]:
 
         if isinstance(index, MultiIndex):
             have_header = any(name for name in index.names)
-            fmt_index = index.format(names=True)
+            fmt_index = index.format(names=True, na_rep=None)
         else:
             have_header = index.name is not None
-            fmt_index = index.format(name=True)
+            fmt_index = index.format(name=True, na_rep=None)
         return fmt_index, have_header
 
     def _get_formatted_values(self) -> list[str]:

pandas/tests/series/test_repr.py

@@ -259,6 +259,16 @@ def test_float_repr(self):
         assert repr(ser) == expected
 
 
+    def test_different_null_objects(self):
+        # GH#45263
+        ser = pd.Series([1,2,3,4], [True, None, np.nan, pd.NaT])
+        result = repr(ser)
+        assert "NaT" in result
+        assert "nan" in result
+        assert "None" in result
+
+
+
 class TestCategoricalRepr:
     def test_categorical_repr_unicode(self):
         # see gh-21002