update docs

Author: jbrockmendel

doc/source/user_guide/categorical.rst

@@ -77,7 +77,7 @@ By passing a :class:`pandas.Categorical` object to a ``Series`` or assigning it
 .. ipython:: python
 
     raw_cat = pd.Categorical(
-        ["a", "b", "c", "a"], categories=["b", "c", "d"], ordered=False
+        [None, "b", "c", "a"], categories=["b", "c", "d"], ordered=False
     )
     s = pd.Series(raw_cat)
     s

pandas/core/arrays/categorical.py

@@ -821,7 +821,7 @@ def categories(self) -> Index:
         >>> ser.cat.categories
         Index(['a', 'b', 'c'], dtype='str')
 
-        >>> raw_cat = pd.Categorical(["a", "b", "c", "a"], categories=["b", "c", "d"])
+        >>> raw_cat = pd.Categorical([None, "b", "c", "a"], categories=["b", "c", "d"])
         >>> ser = pd.Series(raw_cat)
         >>> ser.cat.categories
         Index(['b', 'c', 'd'], dtype='str')
@@ -1129,7 +1129,7 @@ def set_categories(
         For :class:`pandas.Series`:
 
         >>> raw_cat = pd.Categorical(
-        ...     ["a", "b", "c", "A"], categories=["a", "b", "c"], ordered=True
+        ...     ["a", "b", "c", None], categories=["a", "b", "c"], ordered=True
         ... )
         >>> ser = pd.Series(raw_cat)
         >>> ser