Issue #19795: Mark up None as literal text.
diff --git a/Doc/library/imaplib.rst b/Doc/library/imaplib.rst
index 20e377f..18f6d9d 100644
--- a/Doc/library/imaplib.rst
+++ b/Doc/library/imaplib.rst
@@ -90,7 +90,7 @@
 
    Parse an IMAP4 ``INTERNALDATE`` string and return corresponding local
    time.  The return value is a :class:`time.struct_time` instance or
-   None if the string has wrong format.
+   ``None`` if the string has wrong format.
 
 .. function:: Int2AP(num)