Address Serhiy's review

Raise SystemError if event is NULL or if "N" format is used.

Doc/c-api/sys.rst

@@ -298,16 +298,18 @@ accessible to C code.  They all work with the current interpreter thread's
    as used in :c:func:`Py_BuildValue` are available. If the built value is not
    a tuple, it will be added into a single-element tuple.
 
-   :exc:`ValueError` is raised if the ``N`` format is used in *format*. The
-   ``N`` format option consumes a reference, but since there is no way to know
-   whether arguments to this function will be consumed, using it may cause
-   reference leaks.
+   The ``N`` format option must not be used. It consumes a reference, but since
+   there is no way to know whether arguments to this function will be consumed,
+   using it may cause reference leaks.
 
    Note that ``#`` format characters should always be treated as
    :c:type:`Py_ssize_t`, regardless of whether ``PY_SSIZE_T_CLEAN`` was defined.
 
    :func:`sys.audit` performs the same function from Python code.
 
+   Raise :exc:`SystemError` and return *NULL* if *event* is *NULL* or if the
+   ``N`` format option is used.
+
    See also :c:func:`PySys_AuditTuple`.
 
    .. versionadded:: 3.8

Python/sysmodule.c

@@ -214,15 +214,15 @@ sys_audit_tstate(PyThreadState *ts, const char *event,
     }
 
     if (event == NULL) {
-        _PyErr_SetString(ts, PyExc_ValueError,
+        _PyErr_SetString(ts, PyExc_SystemError,
                          "event argument must not be NULL");
         return -1;
     }
 
     /* N format is inappropriate, because you do not know
        whether the reference is consumed by the call. */
     if (argFormat != NULL && strchr(argFormat, 'N')) {
-        _PyErr_SetString(ts, PyExc_ValueError,
+        _PyErr_SetString(ts, PyExc_SystemError,
                          "N format must not be used in the format argument");
         return -1;
     }
@@ -357,18 +357,16 @@ PySys_Audit(const char *event, const char *argFormat, ...)
 int
 PySys_AuditTuple(const char *event, PyObject *args)
 {
-    if (args) {
-        if (!PyTuple_Check(args)) {
-            PyErr_Format(PyExc_TypeError, "args must be tuple, got %s",
-                         Py_TYPE(args)->tp_name);
-            return -1;
-        }
-
-        return PySys_Audit(event, "O", args);
-    }
-    else {
+    if (args == NULL) {
         return PySys_Audit(event, NULL);
     }
+
+    if (!PyTuple_Check(args)) {
+        PyErr_Format(PyExc_TypeError, "args must be tuple, got %s",
+                     Py_TYPE(args)->tp_name);
+        return -1;
+    }
+    return PySys_Audit(event, "O", args);
 }
 
 /* We expose this function primarily for our own cleanup during