Issue #9854: The default read() implementation in io.RawIOBase now
handles non-blocking readinto() returning None correctly.
diff --git a/Doc/library/io.rst b/Doc/library/io.rst
index e61aa90..3e0c62d 100644
--- a/Doc/library/io.rst
+++ b/Doc/library/io.rst
@@ -361,8 +361,9 @@
.. method:: readinto(b)
- Read up to len(b) bytes into bytearray *b* and return the number of bytes
- read.
+ Read up to len(b) bytes into bytearray *b* and return the number ofbytes
+ read. If the object is in non-blocking mode and no bytes are available,
+ ``None`` is returned.
.. method:: write(b)