Add ' '

Author: rruuaanng

Doc/c-api/unicode.rst

@@ -610,7 +610,7 @@ APIs:
 .. c:function:: void PyUnicode_Append(PyObject **p_left, PyObject *right)
 
    Append the string *right* to the end of *p_left*.  (In particular, a :exc:`SystemError`
-   if *p_left* or *right* is NULL, or if either is not a Unicode object).
+   if *p_left* or *right* is ``NULL``, or if either is not a Unicode object).
 
 
 .. c:function:: const char* PyUnicode_GetDefaultEncoding(void)