bpo-38600: NULL -> ``NULL``. (GH-17001)
Also fix some other formatting.
diff --git a/Doc/c-api/arg.rst b/Doc/c-api/arg.rst
index 594fef2..f17c63d 100644
--- a/Doc/c-api/arg.rst
+++ b/Doc/c-api/arg.rst
@@ -345,7 +345,7 @@
If the *converter* returns ``Py_CLEANUP_SUPPORTED``, it may get called a
second time if the argument parsing eventually fails, giving the converter a
chance to release any memory that it had already allocated. In this second
- call, the *object* parameter will be NULL; *address* will have the same value
+ call, the *object* parameter will be ``NULL``; *address* will have the same value
as in the original call.
.. versionchanged:: 3.1