Issue #17176: Document that imp.NullImporter is no longer inserted

into sys.path_importer_cache.

Doc/library/imp.rst

@@ -326,16 +326,17 @@ to indicate the search result of :func:`find_module`.
    with an existing directory or empty string raises :exc:`ImportError`.
    Otherwise, a :class:`NullImporter` instance is returned.
 
-   Python adds instances of this type to ``sys.path_importer_cache`` for any path
-   entries that are not directories and are not handled by any other path hooks on
-   ``sys.path_hooks``.  Instances have only one method:
-
+   Instances have only one method:
 
    .. method:: NullImporter.find_module(fullname [, path])
 
       This method always returns ``None``, indicating that the requested module could
       not be found.
 
+   .. versionchanged:: 3.3
+      ``None`` is inserted into ``sys.path_importer_cache`` instead of an
+      instance of :class:`NullImporter`.
+
 
 .. _examples-imp:
 

Doc/library/sys.rst

@@ -785,12 +785,15 @@ always available.
     A dictionary acting as a cache for :term:`finder` objects. The keys are
     paths that have been passed to :data:`sys.path_hooks` and the values are
     the finders that are found. If a path is a valid file system path but no
-    explicit finder is found on :data:`sys.path_hooks` then ``None`` is
-    stored to represent the implicit default finder should be used. If the path
-    is not an existing path then :class:`imp.NullImporter` is set.
+    finder is found on :data:`sys.path_hooks` then ``None`` is
+    stored.
 
     Originally specified in :pep:`302`.
 
+    .. versionchanged:: 3.3
+       ``None`` is stored instead of :class:`imp.NullImporter` when no finder
+       is found.
+
 
 .. data:: platform