[3.8] bpo-38600: NULL -> ``NULL``. (GH-17001) (GH-17003)
Also fix some other formatting.
(cherry picked from commit e835b31d2b212c3c7820364398979cae2a9740b2)
diff --git a/Doc/extending/extending.rst b/Doc/extending/extending.rst
index 7986ea1..5b32a2c 100644
--- a/Doc/extending/extending.rst
+++ b/Doc/extending/extending.rst
@@ -536,7 +536,7 @@
:c:func:`PyObject_CallObject`. This function has two arguments, both pointers to
arbitrary Python objects: the Python function, and the argument list. The
argument list must always be a tuple object, whose length is the number of
-arguments. To call the Python function with no arguments, pass in NULL, or
+arguments. To call the Python function with no arguments, pass in ``NULL``, or
an empty tuple; to call it with one argument, pass a singleton tuple.
:c:func:`Py_BuildValue` returns a tuple when its format string consists of zero
or more format codes between parentheses. For example::