doc [ci skip]

Author: blueyed

py/_path/local.py

@@ -574,8 +574,10 @@ def chdir(self):
 
     @contextmanager
     def as_cwd(self):
-        """ return context manager which changes to current dir during the
-        managed "with" context. On __enter__ it returns the old dir.
+        """
+        Return a context manager, which changes to the path's dir during the
+        managed "with" context.
+        On __enter__ it returns the old dir, which might be ``None``.
         """
         old = self.chdir()
         try: